Naming Alkynes
Definition of Alkynes :
Alkynes are organic chemical compounds that include a triple covalent bond between two carbon atoms.
That is, alkynes are the class (or "category") of organic hydrocarbon compounds that include a part consisting of two carbon atoms attached to each other by a triple covalent bond, which is usually represented in molecular diagrams as three parallel straight lines between the carbon atoms attached together by that triple bond.
Alkyne molecules can vary in size up to very long molecules most of which consist of carbon atoms attached to each other and also to hydrogen atoms.
Names of Alkynes in General
Alkynes are named according to the same system as other organic compounds, with the suffix -yne used to designate the presence in the molecule of a triple carbon-carbon bond.
The first step is to consider the number of carbon atoms forming a chain. If they are attached together in a linear (i.e. unbranched ) configuration then the number of carbon atoms is indicated according to the same system as used for naming alkanes (see the examples listed in the table below).
However, if the carbon atoms do not form a linear chain but include branches , the longest linear chain of carbon atoms within the molecule determines the base of the name of the compound, onto which is added information about the branches incl. their
lengths in terms of the number of carbon atoms in each branch (i.e. methyl- indicates a branch consisting of just one carbon atom attached to the main chain, ethyl- indicates a branch of two carbon atoms in length, etc.) and their positions along the longest linear carbon chain (e.g. attached to the 2nd carbon, 3rd carbon, etc.).
The simplest linear alkynes are named and their structures drawn in the following table.
Names and Structures of simple Linear Alkynes
The first ten members of the homologous series of linear alkynes with the triple bond attached to the first (=last) carbon atom is shown below.
The simple structures drawn below show bond types such as single and triple bonds, but not accurate bond angles.
Ethyne (C 2 H2 )
Simple Formula:
HCCH
Simple Structure:
* Examples of other / previous names:
acetylene
acetylen
ethenylene
ethine
ethin
vinylene
Propyne (C 3 H4 )
Simple Formula:
CH 3 CCH
Simple Structure:
* Examples of other / previous names:
1-propyne
prop-1-yne
methylacetylene
methyl acetylene
allylene
propylene tetramer
Butyne (C 4 H6 )
Simple Formula:
CH 3 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-butyne
but-1-yne
butyne-1
ethylacetylene
ethyl acetylene
Pentyne (C 5 H8 )
Simple Formula:
CH 3 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-pentyne
pent-1-yne
acetylene
Hexyne (C 6 H10 )
Simple Formula:
CH 3 CH 2 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-hexyne
hex-1-yne
butylacetylene
n-butylacetylene
Heptyne (C 7 H12 )
Simple Formula:
CH 3 CH 2 CH 2 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-heptyne
hept-1-yne
amylacetylene
Octyne (C 8 H14 )
Simple Formula:
CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-octyne
oct-1-yne
hexylacetylene
Nonyne (C 9 H16 )
Simple Formula:
CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-nonyne
non-1-yne
Decyne (C 10 H18 )
Simple Formula:
CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CCH
Simple Structure:
* Examples of other / previous names:
1-decyne
octylacetylene
Why stop at ten carbon atoms (in the chain)? It doesn't.
There are more similar linear alkynes.
*Note : The synonyms indicated for compounds listed above are just some examples of alternative names found online and believed to have been used to refer to the substance indicated. They have not all been verified and may include common (non-scientific) names, trade names specific to particular suppliers, and perhaps errors. The purpose of these lists is to give a general indication of the range of names by which alkynes are known - both generally, and specifically. Knowledge of these alternative names is not usually required for A-Level Chemistry or other school exams.
See also the related page about functional groups in organic molecules , which includes the alkyne group, among others.
Note : This is one of many pages about types of organic compounds in our Organic Chemistry Section. Similar and related pages describe hydrocarbons , alkanes , haloalkanes, alkenes, alkynes , cycloalkanes, aromatic hydrocarbons (arenes), alcohols , esters ,
ethers, aldehydes , ketones , carboxylic acids ,
acid chlorides , acid anhydrides , azo dyes,
amines , amides , nitriles , amino acids (chemistry), peptides, proteins (chemistry), polypeptides and others. If you need further information ask your chemistry tutor.
According to the International Union of Pure and Applied Chemistry (IUPAC) recommendations for nomenclature of organic chemistry, compounds that include the -alkyne group functional group may be called
alkynes .
Saturday 30 December 2017
Alkene
Alkenes contain carbon-carbon double bonds and are unsaturated hydrocarbons with the molecular formula is C H . This is also the same molecular formula as cycloalkanes. Alkenes are named using the same general naming rules for alkanes, except that the suffix is now -ene. There are a few other small differences:
The main chain of carbon atoms must contain both carbons in the double bond. The main chain is numbered so that the double bond gets the smallest number.
Before the root name, the number of the carbon atom at which the double bond starts (the smaller number) is written.
If more than one double bond is present, the prefixes di-, tri-, tetra-, etc. are used before the -ene, and (strangely) the letter "a" is added after the prefix for the number of carbon atoms.
Introduction
Alkenes and alkynes are hydrocarbons which respectively have carbon-carbon double bond and carbon-carbon triple bond functional groups. The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups. Alkenes are named as if they were alkanes, but the "-ane" suffix is changed to "-ene". If the alkene contains only one double bond and that double bond is terminal (the double bond is at one end of the molecule or another) then it is not necessary to place any number in front of the name.
butane: C H (CH CH CH CH )
butene: C H (CH =CHCH
CH )
If the double bond is not terminal (if it is on a carbon somewhere in the center of the chain) then the carbons should be numbered in such a way as to give the first of the two double-bonded carbons the lowest possible number, and that number should precede the "ene" suffix with a dash, as shown below.
correct: pent-2-ene (CH CH=CHCH CH )
incorrect: pent-3-ene (CH CH CH=CHCH )
The second one is incorrect because flipping the formula horizontally results in a lower number for the alkene.
If there is more than one double bond in an alkene, all of the bonds should be numbered in the name of the molecule - even terminal double bonds. The numbers should go from lowest to highest, and be separated from one another by a comma. The IUPAC numerical prefixes are used to indicate the number of double bonds.
octa-2,4-diene: CH CH=CHCH=CHCH CH CH
deca-1,5-diene: CH =CHCH CH CH=CHCH CH CH CH
Note that the numbering of "2-4" above yields a molecule with two double bonds separated by just one single bond. Double bonds in such a condition are called "conjugated", and they represent an enhanced stability of conformation, so they are energetically favored as reactants in many situations and combinations.
Alkane C H This is the maximum H/C ratio for a given number of carbon atoms.
Alkene C H Each double bond reduces the number of hydrogen atoms by 2.
The parent structure is the longest chain containing both carbon atoms of the double bond. The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120° A double bond consists of one sigma bond formed by overlap of sp hybrid orbitals and one pi bond formed by overlap of parallel 2 p orbitals
Figure 1 : (a) The σ-bonded framework is formed by the overlap of two sets of singly occupied carbon sp hybrid orbitals and four singly occupied hydrogen 1s orbitals to form electron-pair bonds. This uses 10 of the 12 valence electrons to form a total of five σ bonds (four C–H bonds and one C–C bond). (b) One singly occupied unhybridized 2p orbital remains on each carbon atom to form a carbon–carbon π bond. (Note: by convention, in planar molecules the axis perpendicular to the molecular plane is the z-axis.)
The molecular formula of a hydrocarbon provides information about the possible structural types it may represent. For example, consider compounds having the formula C H . The formula of the five-carbon alkane pentane is C H so the difference in hydrogen content is 4. This difference suggests such compounds may have a triple bond, two double bonds, a ring plus a double bond, or two rings. Some examples are shown here, and there are at least fourteen others!
IUPAC Rules for Alkene and Cycloalkene Nomenclature
1. The ene suffix (ending) indicates an alkene or cycloalkene.
2. The longest chain chosen for the root name must include both carbon atoms of the double bond .
3. The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
4. The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
5. In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
6. Substituent groups containing double bonds are:
H C=CH– Vinyl group
H C=CH–CH – Allyl group
EXAMPLE 1
In this diagram this is a cis conformation. It has both the substituents going upward. This molecule would be called (cis) 5-chloro-3-heptene.)
Trans would look like this
v. On the other hand if there are 3 or 4 non-hydrogen different atoms attached to the alkene then use the E, Z system.
E (entgegen) means the higher priority groups are opposite one another relative to the double bond.
Z (zusammen) means the higher priority groups are on the same side relative to the double bond.
(You could think of Z as Zame Zide to help memorize it.)
EXAMPLE 2
Solution
In this example it is E-4-chloro-3-heptene. It is E because the Chlorine and the CH CH are the two higher priorities and they are on opposite sides.
vi. A hydroxyl group gets precedence over th double bond. Therefore alkenes containing alchol groups are called alkenols. And the prefix becomes --enol. And this means that now the alcohol gets lowest priority over the alkene.
vii. Lastly remember that alkene substituents are called alkenyl. Suffix --enyl.
Here is a chart containing the systemic name for the first twenty straight chain alkenes.
Name Molecular formula
Ethene C H
Propene C H
Butene C H
Pentene C H
Hexene C H
Heptene C H
Octene C H
Nonene C H
Decene C H
Undecene C H
Dodecene C H
Tridecene C H
Tetradecene C H
Pentadecene C H
Hexadecene C H
Heptadecene C H
Octadecene C H
Nonadecene C H
Eicosene C H
Did you notice how there is no methene? Because it is impossible for a carbon to have a double bond with nothing.
Geometric Isomers
Double bonds can exist as geometric isomers and these isomers are designated by using either the cis / trans designation or the modern E / Z designation.
cis Isomers
.The two largest groups are on the same side of the double bond.
trans Isomers
...The two largest groups are on opposite sides of the double bond.
E/Z nomenclature
E = entgegan ("trans") Z = zusamen ("cis")
Priority of groups is based on the atomic mass of attached atoms (not the size of the group). An atom attached by a multiple bond is counted once for each bond.
fluorine atom > isopropyl group > n-hexyl group
deuterium atom > hydrogen atom
-CH -CH=CH > -CH CH CH
EXAMPLE 3
Try to name the following compounds using both conventions...
Common names
Remove the -ane suffix and add -ylene. There are a couple of unique ones like ethenyl's common name is vinyl and 2-propenyl's common name is allyl. That you should know are...
vinyl substituent H C=CH-
allyl substituent H C=CH-CH -
allene molecule H C=C=CH
isoprene
Endocyclic Alkenes
Endocyclic double bonds have both carbons in the ring and exocyclic double bonds have only one carbon as part of the ring.
Cyclopentene is an example of an endocyclic double bond.
Methylenecylopentane is an example of an exocyclic double bond.
Name the following compounds...
1-methylcyclobutene. The methyl group places the double bond. It is correct to also name this compound as 1-methylcyclobut-1-ene.
1-ethenylcyclohexene, the methyl group places the double bond. It is correct to also name this compound as 1-ethenylcyclohex-1-ene. A common name would be 1-vinylcyclohexene.
Try to draw structures for the following compounds...
2-vinyl-1,3-cyclohexadiene
Outside links
http://www.vanderbilt.edu/AnS/Chemis...0a/alkenes.pdf
References
1. Vollhardt, Peter, and Neil E. Schore.
Organic Chemistry: Structure and Function . 5th Edition. New York: W. H. Freeman & Company, 2007.
Problems
Try to name the following compounds...
1-pentene or pent-1-ene
2-ethyl-1-hexene or 2-ethylhex-1-ene
Try to draw structures for the following compounds...
2-pentene
CH –CH=CH–CH –CH
3-heptene
CH –CH –CH=CH–CH –CH –CH
b. Give the double bond the lowest possible numbers regardless of substituent placement.
• Try to name the following compound...
J
• Try to draw a structure for the following compound...
4-methyl-2-pentene J
Name the following structures:
v. Draw (Z)-5-Chloro-3-ethly-4-hexen-2-ol.
Answers
I. trans-8-ethyl-3-undecene
II. E-5-bromo-4-chloro-7,7-dimethyl-4-undecene
III. Z-1,2-difluoro-cyclohexene
IV. 4-ethenylcyclohexanol.
The main chain of carbon atoms must contain both carbons in the double bond. The main chain is numbered so that the double bond gets the smallest number.
Before the root name, the number of the carbon atom at which the double bond starts (the smaller number) is written.
If more than one double bond is present, the prefixes di-, tri-, tetra-, etc. are used before the -ene, and (strangely) the letter "a" is added after the prefix for the number of carbon atoms.
Introduction
Alkenes and alkynes are hydrocarbons which respectively have carbon-carbon double bond and carbon-carbon triple bond functional groups. The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups. Alkenes are named as if they were alkanes, but the "-ane" suffix is changed to "-ene". If the alkene contains only one double bond and that double bond is terminal (the double bond is at one end of the molecule or another) then it is not necessary to place any number in front of the name.
butane: C H (CH CH CH CH )
butene: C H (CH =CHCH
CH )
If the double bond is not terminal (if it is on a carbon somewhere in the center of the chain) then the carbons should be numbered in such a way as to give the first of the two double-bonded carbons the lowest possible number, and that number should precede the "ene" suffix with a dash, as shown below.
correct: pent-2-ene (CH CH=CHCH CH )
incorrect: pent-3-ene (CH CH CH=CHCH )
The second one is incorrect because flipping the formula horizontally results in a lower number for the alkene.
If there is more than one double bond in an alkene, all of the bonds should be numbered in the name of the molecule - even terminal double bonds. The numbers should go from lowest to highest, and be separated from one another by a comma. The IUPAC numerical prefixes are used to indicate the number of double bonds.
octa-2,4-diene: CH CH=CHCH=CHCH CH CH
deca-1,5-diene: CH =CHCH CH CH=CHCH CH CH CH
Note that the numbering of "2-4" above yields a molecule with two double bonds separated by just one single bond. Double bonds in such a condition are called "conjugated", and they represent an enhanced stability of conformation, so they are energetically favored as reactants in many situations and combinations.
Alkane C H This is the maximum H/C ratio for a given number of carbon atoms.
Alkene C H Each double bond reduces the number of hydrogen atoms by 2.
The parent structure is the longest chain containing both carbon atoms of the double bond. The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120° A double bond consists of one sigma bond formed by overlap of sp hybrid orbitals and one pi bond formed by overlap of parallel 2 p orbitals
Figure 1 : (a) The σ-bonded framework is formed by the overlap of two sets of singly occupied carbon sp hybrid orbitals and four singly occupied hydrogen 1s orbitals to form electron-pair bonds. This uses 10 of the 12 valence electrons to form a total of five σ bonds (four C–H bonds and one C–C bond). (b) One singly occupied unhybridized 2p orbital remains on each carbon atom to form a carbon–carbon π bond. (Note: by convention, in planar molecules the axis perpendicular to the molecular plane is the z-axis.)
The molecular formula of a hydrocarbon provides information about the possible structural types it may represent. For example, consider compounds having the formula C H . The formula of the five-carbon alkane pentane is C H so the difference in hydrogen content is 4. This difference suggests such compounds may have a triple bond, two double bonds, a ring plus a double bond, or two rings. Some examples are shown here, and there are at least fourteen others!
IUPAC Rules for Alkene and Cycloalkene Nomenclature
1. The ene suffix (ending) indicates an alkene or cycloalkene.
2. The longest chain chosen for the root name must include both carbon atoms of the double bond .
3. The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
4. The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
5. In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
6. Substituent groups containing double bonds are:
H C=CH– Vinyl group
H C=CH–CH – Allyl group
EXAMPLE 1
In this diagram this is a cis conformation. It has both the substituents going upward. This molecule would be called (cis) 5-chloro-3-heptene.)
Trans would look like this
v. On the other hand if there are 3 or 4 non-hydrogen different atoms attached to the alkene then use the E, Z system.
E (entgegen) means the higher priority groups are opposite one another relative to the double bond.
Z (zusammen) means the higher priority groups are on the same side relative to the double bond.
(You could think of Z as Zame Zide to help memorize it.)
EXAMPLE 2
Solution
In this example it is E-4-chloro-3-heptene. It is E because the Chlorine and the CH CH are the two higher priorities and they are on opposite sides.
vi. A hydroxyl group gets precedence over th double bond. Therefore alkenes containing alchol groups are called alkenols. And the prefix becomes --enol. And this means that now the alcohol gets lowest priority over the alkene.
vii. Lastly remember that alkene substituents are called alkenyl. Suffix --enyl.
Here is a chart containing the systemic name for the first twenty straight chain alkenes.
Name Molecular formula
Ethene C H
Propene C H
Butene C H
Pentene C H
Hexene C H
Heptene C H
Octene C H
Nonene C H
Decene C H
Undecene C H
Dodecene C H
Tridecene C H
Tetradecene C H
Pentadecene C H
Hexadecene C H
Heptadecene C H
Octadecene C H
Nonadecene C H
Eicosene C H
Did you notice how there is no methene? Because it is impossible for a carbon to have a double bond with nothing.
Geometric Isomers
Double bonds can exist as geometric isomers and these isomers are designated by using either the cis / trans designation or the modern E / Z designation.
cis Isomers
.The two largest groups are on the same side of the double bond.
trans Isomers
...The two largest groups are on opposite sides of the double bond.
E/Z nomenclature
E = entgegan ("trans") Z = zusamen ("cis")
Priority of groups is based on the atomic mass of attached atoms (not the size of the group). An atom attached by a multiple bond is counted once for each bond.
fluorine atom > isopropyl group > n-hexyl group
deuterium atom > hydrogen atom
-CH -CH=CH > -CH CH CH
EXAMPLE 3
Try to name the following compounds using both conventions...
Common names
Remove the -ane suffix and add -ylene. There are a couple of unique ones like ethenyl's common name is vinyl and 2-propenyl's common name is allyl. That you should know are...
vinyl substituent H C=CH-
allyl substituent H C=CH-CH -
allene molecule H C=C=CH
isoprene
Endocyclic Alkenes
Endocyclic double bonds have both carbons in the ring and exocyclic double bonds have only one carbon as part of the ring.
Cyclopentene is an example of an endocyclic double bond.
Methylenecylopentane is an example of an exocyclic double bond.
Name the following compounds...
1-methylcyclobutene. The methyl group places the double bond. It is correct to also name this compound as 1-methylcyclobut-1-ene.
1-ethenylcyclohexene, the methyl group places the double bond. It is correct to also name this compound as 1-ethenylcyclohex-1-ene. A common name would be 1-vinylcyclohexene.
Try to draw structures for the following compounds...
2-vinyl-1,3-cyclohexadiene
Outside links
http://www.vanderbilt.edu/AnS/Chemis...0a/alkenes.pdf
References
1. Vollhardt, Peter, and Neil E. Schore.
Organic Chemistry: Structure and Function . 5th Edition. New York: W. H. Freeman & Company, 2007.
Problems
Try to name the following compounds...
1-pentene or pent-1-ene
2-ethyl-1-hexene or 2-ethylhex-1-ene
Try to draw structures for the following compounds...
2-pentene
CH –CH=CH–CH –CH
3-heptene
CH –CH –CH=CH–CH –CH –CH
b. Give the double bond the lowest possible numbers regardless of substituent placement.
• Try to name the following compound...
J
• Try to draw a structure for the following compound...
4-methyl-2-pentene J
Name the following structures:
v. Draw (Z)-5-Chloro-3-ethly-4-hexen-2-ol.
Answers
I. trans-8-ethyl-3-undecene
II. E-5-bromo-4-chloro-7,7-dimethyl-4-undecene
III. Z-1,2-difluoro-cyclohexene
IV. 4-ethenylcyclohexanol.
Definition of alkane
Alkanes are chemical compounds that consist only of the elements carbon (C) and hydrogen (H) linked exclusively by single bonds.
Each carbon atom forms 4 bonds (either C-H or C-C bonds). Each hydrogen atom is connected to a single carbon atom, by a H-C bond.
Alkanes are one of the simplest types of
organic compounds and are therefore generally taught early in basic courses in organic chemistry, e.g. at GCSE level in UK schools.
Alkanes are hydrocarbons because they consist only of carbon and hydrogen atoms.
These atoms combine in proportions according to the general formula to form
alkanes :
C n H2n+2
where the letter n represents the number of carbon atoms in each molecule of the compound.
In general there are three basic types of alkanes.
They are:
linear alkanes ,
branched alkanes and
cyclic alkanes (which may also be referred to as cycloalkanes).
Of these, linear alkanes are the simplest to draw and explain and are therefore usually the first to be introduced in chemistry lessons.
Linear Alkanes:
The homologous series of linear alkanes is illustrated in the following table:
Methane (CH 4 )
Number of carbon atoms: 1
Simple Structure:
* Examples of other / previous names:
natural gas
marsh gas
methyl hydride
Number of isomers: 1
Ethane (C 2 H6 )
Number of carbon atoms: 2
Simple Structure:
* Examples of other / previous names:
dimethyl
methyl methane
ethyl hydride
Number of isomers: 1
Propane (C 3 H8 )
Number of carbon atoms: 3
Simple Structure:
* Examples of other / previous names:
dimethyl methane
propyl hydride
Number of isomers: 1
n- Butane (C 4 H10 )
Number of carbon atoms: 4
Simple Structure:
* Examples of other / previous names:
methylethyl methane
butyl hydride
Number of isomers: 2
n- Pentane (C 5 H12 )
Number of carbon atoms: 5
Simple Structure:
* Examples of other / previous names:
amyl hydride
Skellysolve A
Number of isomers: 3
n- Hexane (C 6 H14 )
Number of carbon atoms: 6
Simple Structure:
* Examples of other / previous names:
dipropyl
Gettysolve-B
hexyl hydride
Skellysolve B
Number of isomers: 5
n- Heptane (C 7 H16 )
Number of carbon atoms: 7
Simple Structure:
* Examples of other / previous names:
dipropyl methane
Gettysolve-C
heptyl hydride
Skellysolve C
Number of isomers: 9
n- Octane (C 8 H18 )
Number of carbon atoms: 8
Simple Structure:
* Examples of other / previous names:
dibutyl
octyl hydride
Number of isomers: 18
n- Nonane (C 9 H20 )
Number of carbon atoms: 9
Simple Structure:
* Examples of other / previous names:
nonyl hydride
Shellsol 140
Number of isomers: 35
n- Decane (C 10 H22 )
Number of carbon atoms: 10
Simple Structure:
* Examples of other / previous names:
decyl hydride
Number of isomers: 75
Why stop at ten carbon atoms (in the chain)? It doesn't.
There are more similar linear alkanes.
*Note : The synonyms indicated for compounds listed above are just some examples of alternative names found online and believed to have been used to refer to the substance indicated. They have not all been verified and may include common (non-scientific) names, trade names specific to particular suppliers, and perhaps errors. The purpose of these lists is to give a general indication of the range of names by which alkanes are known - both generally, and specifically. Knowledge of these alternative names is not usually required for A-Level Chemistry or other school exams.
In the case of the names of alkanes beginning with n- , the n- part is included to specify the linear (as opposed to a branched or cyclic) form of that particular alkane. In some cases the atoms may be arranged in different ways, hence the alkane may exist in the forms of several different structural isomers . Some examples of structural isomers are shown below.
Branched Alkanes:
Alkane molecules that include more than 3 carbon atoms can be arranged in more than one way. The simplest example is butane, which can take either of two different forms called structural isomers , as shown below.
The 2 Structural Isomers of Butane
* In reality molecules occupy 3-dimensional space so 2-dimensional representations such as those above are simplifications. The type of representations shown here are sufficient to distinguish between linear- and the different types of branched- alkanes. The molecular diagrams above are intended to represent only which atoms are linked ("bonded") with which other atoms and not to indicate the positions, e.g. angles, between atoms as they occur in nature. Such simplification is necessary in order to describe and explain increasingly complex organic structures.
Another way to draw methylpropane that is less accurate, but perhaps easier to see initially, is :
The diagram above may be thought of as the result of exchanging the carbon-group on the right-hand-side of the n-butane structure with the hydrogen atom indicated. However, the diagram of the structure of methylpropane (above) is not an accurate representation of the actual molecule because the angles between the atoms in real 3-dimensional space are more similar to each other, as indicated in the molecular structure shown in the smaller diagram further above.
It is useful to be aware of structural isomers of organic molecules as the result of exchanging the positions of certain atoms and/or groups because this concept applies to many different types of organic molecules, not just to alkanes - which include the simplest examples, such as butane and methylpropane .
Another note about the diagrams above is that, because they are very simple representations of the arrangements of atoms within molecules, the lengths and thicknesses of the lines representing chemical bonds do not generally signify anything about the bonds they represent. Although it is a good idea to draw these lines as consistently as possible, it is not unusual to need to vary the lengths slightly in order to fit within the space available.
In molecular diagrams of organic molecules
single lines represent single bonds , double lines represent double bonds , and triple lines represent triple bonds . The molecular diagrams on this page all include only single bonds , which shows that alkanes are saturated molecules.
The 3 Structural Isomers of Pentane
Pentane is an alkane that has 5 carbon atoms in each molecule. In organic chemistry generally, the larger the molecule, the more different ways in which the atoms can join together.
There are 3 different structural isomers of pentane, as shown below:
* In reality molecules occupy 3-dimensional space so 2-dimensional representations such as those above are simplifications. The type of representations shown here are sufficient to distinguish between linear- and the different types of branched- alkanes. The molecular diagrams above are intended to represent only which atoms are linked ("bonded") with which other atoms and not to indicate the positions, e.g. angles, between atoms as they occur in nature. Such simplification is necessary in order to describe and explain increasingly complex organic structures.
As indicated in the right-hand column of the table of linear alkanes further up this page, molecules of alkanes that have more carbon atoms per molecule can exist in many more different isomeric forms. Introductory courses, such as GCSE Chemistry, do not usually require detailed knowledge of all the isomers of the larger alkanes but it can be useful to work out and draw the molecular diagrams of some them in order to aid understanding and memory of the concept of structural isomerism .
More about alkanes generally
(Revision Notes):
Alkanes form a homologous series of organic compounds (meaning that all alkanes can be described by a single general chemical formula, specifically C n H2n+2 in the case of alkanes) in which the members of the series differ by a constant relative molecular mass of 14, which is the molecular mass of one carbon atom and two hydrogen atoms.
Alkanes are saturated compounds, meaning that the atoms that form the molecules of alkane compounds are linked exclusively by single bonds .
There is no limit to the number of carbon atoms that can be linked together in such a way as to form a linear alkane.
The conditions that alkane molecules must satisfy are that they are:
1. hydrocarbons (only contain atoms of carbon and hydrogen),
2. saturated (only contain single bonds; so include no double- or triple- carbon bonds),
3. linear alkanes (specifically) are
acyclic , meaning that the carbon atoms are generally connected in such a way as to form a line, if so arranged , rather than a ring ... which would be a cycloalkane .
Saturated oils and waxes are examples of larger alkanes in which the number of carbon atoms in the carbon chain , which is sometimes called a " carbon backbone ", is greater than 10.
Alkanes are not very reactive and have little biological activity.
However, alkanes are sometimes described in terms of being a "molecular tree" (i.e. a basic structure) onto which more complex and biologically active atoms or "functional groups" of atoms may be attached, the simplest example being halogenoalkanes (also known as haloalkanes)
Tuesday 19 December 2017
Source of organic compounds
SOURCES OF ORGANIC COMPOUNDS.
All organic compounds aat one time came from plants or animals.many of our most importants substance are still derived from these sources directly or indirectly.
1) PLANTS AND ANIMALS
Many organic compounds are obtained directly from plant and animals sources by suitable. method of isllation.a few familiar EXAMPLE are carbohydrates (cellulose, sugar, and starches.) proteins (silk, wool, casein, and food proteins) fats and oils(cottonsed soybean oils lard, butter) alkaloids (quinine ,morphine, strychnine) hormones, vitamins,perfumes, flavours and resins.
2) NATURAL GAS AND PETROLEUM.
Natural gas and petroleum are now the major sourcse of organic compounds .they are used as fuels and also, throughsynthetic organic reaction.for the production of hundreds of useful organic substances such as solvents,synthetic rubber,explosive,and plastic.
3) COAL
Coal is another major sources of organic compounds.it yield coke and coal-tar on pyrolysis or destructive distillation.more then 200 organic compounds have been directly isolated from coal-tar. these coal-tar products from the starting materialsfor the manufacture of thousands of useful aromatic compounds,including pefumes,drugs,dyes, photographic developers,and other.
4) SYNTHESIS.
Simple organic compunds derived from petroleum or coal have been converted into thousands of useful materials by synthetic mthod.many EXAMPLE might be cited of syntgetic organic compounds replacing those obtained from natural sources,such as dyes, rubber, fibres, plastic ,drugs, vitamins.in many cases the synthetic materials are superior to the natural compounds replaced.for example ,synthetic dyes are superior to those of natural origin.in other cases the synthetic materials are entirely unknown in nature and fill the requirements not satisfied are entirely other sources.EXAMPLE.are ether .glycol, aspirin, and sulpher drugs.synthetic organicchemistry touches almost every phase of life.
1) PLANTS AND ANIMALS
Many organic compounds are obtained directly from plant and animals sources by suitable. method of isllation.a few familiar EXAMPLE are carbohydrates (cellulose, sugar, and starches.) proteins (silk, wool, casein, and food proteins) fats and oils(cottonsed soybean oils lard, butter) alkaloids (quinine ,morphine, strychnine) hormones, vitamins,perfumes, flavours and resins.
2) NATURAL GAS AND PETROLEUM.
Natural gas and petroleum are now the major sourcse of organic compounds .they are used as fuels and also, throughsynthetic organic reaction.for the production of hundreds of useful organic substances such as solvents,synthetic rubber,explosive,and plastic.
3) COAL
Coal is another major sources of organic compounds.it yield coke and coal-tar on pyrolysis or destructive distillation.more then 200 organic compounds have been directly isolated from coal-tar. these coal-tar products from the starting materialsfor the manufacture of thousands of useful aromatic compounds,including pefumes,drugs,dyes, photographic developers,and other.
4) SYNTHESIS.
Simple organic compunds derived from petroleum or coal have been converted into thousands of useful materials by synthetic mthod.many EXAMPLE might be cited of syntgetic organic compounds replacing those obtained from natural sources,such as dyes, rubber, fibres, plastic ,drugs, vitamins.in many cases the synthetic materials are superior to the natural compounds replaced.for example ,synthetic dyes are superior to those of natural origin.in other cases the synthetic materials are entirely unknown in nature and fill the requirements not satisfied are entirely other sources.EXAMPLE.are ether .glycol, aspirin, and sulpher drugs.synthetic organicchemistry touches almost every phase of life.
Understand the Difference Between Organic and Inorganic
Difference between organic and inorganic compounds
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The word "organic" means something very different in chemistry than it does when you're talking about produce and food. Organic compounds and inorganiccompounds form the basis of chemistry. The primary difference between organic compounds and inorganic compounds is that organic compounds always contain carbon while most inorganic compounds do not contain carbon. Also, nearly all organic compounds contain carbon-hydrogen or C-H bonds.
Note, containing carbon is not sufficientfor a compound to be considered organic! Look for both carbon and hydrogen.
Organic and inorganic chemistry are two of the main disciplines of chemistry. An organic chemist studies organic molecules and reactions, while an inorganic chemistry focuses on inorganic reactions.
EXAMPLES OF ORGANIC COMPOUNDS OR MOLECULES
Molecules associated with living organisms are organic. These include nucleic acids, fats, sugars, proteins, enzymes and hydrocarbon fuels. All organic molecules contain carbon, nearly all contain hydrogen, and many also contain oxygen.
- DNA
- table sugar or sucrose, C12H22O11
- benzene, C6H6
- methane, CH4
- ethanol or grain alcohol, C2H6O
EXAMPLES OF INORGANIC COMPOUNDS
Inorganics include salts, metals, substances made from single elements and any other compounds that don't contain carbon bonded to hydrogen. Some inorganic molecules do, in fact, contain carbon.
- table salt or sodium chloride, NaCl
- carbon dioxide, CO2
- diamond (pure carbon)
- silver
- sulfur
ORGANIC COMPOUNDS WITHOUT C-H BONDS
There are few organic compounds that don't contain carbon-hydrogen bonds. Examples of these exceptions include:
- carbon tetrachloride (CCl4)
- urea [CO(NH2)2]
ORGANIC COMPOUNDS AND LIFE
While most organic compounds encountered in chemistry are produced by living organisms, it's possible for the molecules to form through other processes.
For example, when scientists talk about organic molecules discovered on Pluto, this doesn't mean there are aliens on the world. Solar radiation can provide energy to produce organic compounds from inorganic carbon compounds.
What is the meaning of "vital force theory" in organic chemistry
What is the meaning of "vital force theory" in organic chemistry?
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In 1815 AD, a Swedish chemist J.J. Berzelius put forward vital force theory to explain the origin of organic compound. According to this theory, organic compound are formed and synthesized only within living species( plants and animals ). The word ‘vital’ is derives from Latin term ‘vita’ which means life. This theory emphasizes on a special force or a living force or presence of life as basic requirement for formation of organic compounds. This theory does not account synthesis of organic compounds in laboratory.
However, in 1828 AD, a German chemist Friedrich Wohlev synthesized organic compound ‘urea’ from simple inorganic compounds like NH4Cl (ammonium chloride) and KCNO ( potassium cynate ). This theory defied the vital force theory.
NH4Cl + KCNO ———————→ NH4CNO +KCl
The right hand side is urea organic compound ).
Organic Chemistry | Definition of Organic Chemistry
Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, which include not only hydrocarbons but also compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon–hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur. This branch of chemistry was originally limited to compounds produced by living organisms but has been broadened to include human-made substances such as plastics. The range of application of organic compounds is enormous and also includes, but is not limited to, pharmaceuticals, petrochemicals, food, explosives, paints, and cosmetics.
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