Major Topics
Structural isomerism
Stereo isomerism
Structural isomerism is further classifed as
Chain or Nuclear Isomerism
Functional isomerism
Metamerism
Tautomerism
Sterio isomerism is further classfied as
Geometrical isomerism
Optical isomerism, enantiomerism or d,l isomerism
Geometrical isomerism - E and Z configuration
Optical isomerism has the follwing concenpts
Diastereomer
erthroenantiomers
Threoenantiomers
Meso compound
Racemic mixture
R and S configuration
Conformations
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Rabu, 24 Desember 2008
Senin, 28 Januari 2008
Revision Alkenes Isomerism
Isomerism in alkenes
1. Structural isomerism: Alkenes show chain isomerism and position isomerism.
a. Chain isomerism: C-4H-8 exists as two chain isomers, n-Butene and Isobutene.
b. Position isomerism: The isomers differ in the position of the double bonds. C-4H-8 can have the double bond as the terminal bond or it can be in the middle. The one with the terminal bond is n-Butene and the one with the double bond in the middle is but-2-ene. Thus butane with the structural formula C-4H-8 has three structural isomers.
2. Geometrical isomerism: Alkenes exhibit geometrical isomerism.
Molecules of the type C2A2B2 are available as geometrical isomers. The two atoms attached to the same carbon atom are different. In this symbols, A and B are different.
The molecule in which similar atons or groups lie on the same side of the double bond is called cis-isomer. Both As are attached to the carbon on one side of the double bond. Simiarly two Bs.
If they are attached on the opposite sides, it is a trans-isomer
Examples
CH3HC=CHCH3 exhibits geometrical isomerism.
As CH3 and H are different groups
Maleic acid and Fumaric acid are geometrical isomers.
HOOCHC=CHCOOH
Cis isomer is maleic acid and trans isomer is fumaric acid.
If they are attached on the opposite sides, it is a trans-isomer
1. Structural isomerism: Alkenes show chain isomerism and position isomerism.
a. Chain isomerism: C-4H-8 exists as two chain isomers, n-Butene and Isobutene.
b. Position isomerism: The isomers differ in the position of the double bonds. C-4H-8 can have the double bond as the terminal bond or it can be in the middle. The one with the terminal bond is n-Butene and the one with the double bond in the middle is but-2-ene. Thus butane with the structural formula C-4H-8 has three structural isomers.
2. Geometrical isomerism: Alkenes exhibit geometrical isomerism.
Molecules of the type C2A2B2 are available as geometrical isomers. The two atoms attached to the same carbon atom are different. In this symbols, A and B are different.
The molecule in which similar atons or groups lie on the same side of the double bond is called cis-isomer. Both As are attached to the carbon on one side of the double bond. Simiarly two Bs.
If they are attached on the opposite sides, it is a trans-isomer
Examples
CH3HC=CHCH3 exhibits geometrical isomerism.
As CH3 and H are different groups
Maleic acid and Fumaric acid are geometrical isomers.
HOOCHC=CHCOOH
Cis isomer is maleic acid and trans isomer is fumaric acid.
If they are attached on the opposite sides, it is a trans-isomer
Minggu, 27 Januari 2008
IIT JEE Revision Alkynes Isomerism
Alkynes exhibit and chain isomerism and position isomerism
Chain isomerism
The arrangement of the chain is different in these isomers
Ex: Pent-1-yne Linear chain pentyne with triple bond at the terminal carbon.
3-Methylbut-1-yne - branched isomer having a methyl group at the 3rd carbon and triple at the terminal carbon.
Position isomerism - position of triple bond changes. Alkynes having more than four carbon atoms exhibit this isomerism.
1-Alkyne 2 Alkyne
Alkynes do not have geometrical isomerism as the bond angle is 180°
Chain isomerism
The arrangement of the chain is different in these isomers
Ex: Pent-1-yne Linear chain pentyne with triple bond at the terminal carbon.
3-Methylbut-1-yne - branched isomer having a methyl group at the 3rd carbon and triple at the terminal carbon.
Position isomerism - position of triple bond changes. Alkynes having more than four carbon atoms exhibit this isomerism.
1-Alkyne 2 Alkyne
Alkynes do not have geometrical isomerism as the bond angle is 180°
Sabtu, 26 Januari 2008
IIT JEE Revision - Amines - Isomerism
1. Chain
Aliphatic amines containing four or more carbon atoms show chain isomerism as branched and straight chain alkyl groups can be attached to the nitrogen atom.
Example: Butan-1-amine, 2-Methylpropan-1-amine, and 2 Methylpropan-2-amine are chain isomers.
2. Position Isomerism
The amino group can be bonded to different carbon atoms of the alkyl group.
Example: Propan-1-amine and Propan-2-amine
3. Functional
Primary, secondary and tertiary amines having the same molecular formula are isomers. This isomerism is functional isomerism because different alkyl groups (functional groups) are present in the molecules and give rise to isomerism
4. Metamerism
In amines metamerism, a type of isomerism in which different alkyl groups are attached to the Nitrogen atom of the amino group exists(molecular formula for isomers is same).
Example: Diethylamine, Methyl-n-propylamine, and Isopropylmethylamine are metamers.
5. Chiral amines
Nitrogen atom undergoes sp3 hybridisation. Hence secondary and tertiary amines have a chiral nitrogen atom. But chiral amines cannot be resolved. This is because the two enantiomeric forms rapidly interconvert and it is very difficult to isolate a pure sample of either enantiomer.
Aliphatic amines containing four or more carbon atoms show chain isomerism as branched and straight chain alkyl groups can be attached to the nitrogen atom.
Example: Butan-1-amine, 2-Methylpropan-1-amine, and 2 Methylpropan-2-amine are chain isomers.
2. Position Isomerism
The amino group can be bonded to different carbon atoms of the alkyl group.
Example: Propan-1-amine and Propan-2-amine
3. Functional
Primary, secondary and tertiary amines having the same molecular formula are isomers. This isomerism is functional isomerism because different alkyl groups (functional groups) are present in the molecules and give rise to isomerism
4. Metamerism
In amines metamerism, a type of isomerism in which different alkyl groups are attached to the Nitrogen atom of the amino group exists(molecular formula for isomers is same).
Example: Diethylamine, Methyl-n-propylamine, and Isopropylmethylamine are metamers.
5. Chiral amines
Nitrogen atom undergoes sp3 hybridisation. Hence secondary and tertiary amines have a chiral nitrogen atom. But chiral amines cannot be resolved. This is because the two enantiomeric forms rapidly interconvert and it is very difficult to isolate a pure sample of either enantiomer.
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