Isomers

Question 1

Constitutional/structural isomers

Answer 1

Chain isomerism
Positional isomerism
Functional group isomerism

same molecular formula different structural formula

Question 2

Chain isomerism

Answer 2

different arrangement of carbon skeleton

Question 3

Positional isomerism

Answer 3

different location of substitutional/functional groups on C chain

Question 4

Functional group isomerism

Answer 4

different functional groups

Question 5

Stereoisomerism

Answer 5

Criteria
Presence of chiral center
cis trans isomerism

same molecular and structural formula but different spatial 3d arrangement of atoms

Question 6

chain and positional isomers

Answer 6

have different physical properties due to difference in SA of contact between molecule but have the same chemical properties due to the fact that they have the same functional group

Question 7

Functional group isomers

Answer 7

types
1. alcohols (OH), ethers(OCH3)
CnH2n+2O
2. alkenes and cycloalkenes 
CnH2n
3.carboxylic acids(OH-C=O) and esters(O-C=O)
CnH2nO2
4. aldehydes(H-C=O )and ketones( CH3-C=O)
CnH2nO

have different physical and chemical properties

Question 8

Cis trans isomerism

Answer 8

two conditions for it to exist
restricted rotation about a bond can be due to
1. C=C in a str8 chain
2. Ring structure
two different groups on each of the carbon atoms with restricted atoms
3. cyclic alkenes do not exhibit cis trans despite fulfilling both conditions

Question 9

cis isomers

Answer 9

have identical atoms groups of atoms on the same side of the double but never on the same carbon

Question 10

trans isomers

Answer 10

have identical atoms/groups of atoms on diagonal sides of the double bond

Question 11

Properties of cis trans isomers

Answer 11

same chemical but different physical

1.due to differences in polarity

Question 12

Molecules containing two or more cis trans

Answer 12

a molecule with ‘m’ cis trans C=C has a max of 2^m stereoisomers

Question 13

Optical isomers/enantiomers

Answer 13

exists when molecules contain at least one chiral centre causing them to lack a point and plane symmetries

Question 14

Chirality

Answer 14

if C atom is attached to 4 diff atoms/groups of atoms

labelled with a *

Question 15

Enantiomers

Answer 15

pair of compounds with same connectivity but opposite 3d shapes. non superimposable images mirror images of each others

Question 16

Properties of optical isomers

Answer 16

1. enantiomers
   rotate the plane of plane polarised light by equal angles in the opposite directions when equal conc of enantiomers are being analysed
   similar chemical properties(exc when interacting w a chiral mol.) and physical properties(exc in the direction in which they rotate plan polarised light)
   different
   different biological properties

2.racemic mixture
mixture containing equal conc of enantiomers the equal but opp rotation of plane polarised light by each enantiomers results in net zero optical activity. mixture is optically inactive despite having chiral molecules

Question 17

Molecules containing two or more chiral centers

Answer 17

a molecule with n chiral centers has a max of 2^n stereoisomers

Question 18

there are some molecules with 2 chiral centers with less than 4 stereoisomers

Answer 18

• might have isomers that are identical/superimposable

Question 19

Meso compound

Answer 19

contains 2 chiral centers but is superimposable on its mirror image as it has a plane of symmetry
optically inactive as the effect on the plane polarised light by each half of the mol. is equal in magnitude but opposite in directions. Hence they cancel each other out to give a net zero effect on plane polarised light

Question 20

in general a molecule with m C=C bonds that exhibit cis-trans isomerism and n chiral centers has a max of 2^m+n stereoisomers

Answer 20

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Question 21

Biological properties of optical isomers

Answer 21

the arrangement of atoms between a pair of enantiomers are recognised

1. enantiomers can interact differently with the chiral receptor cells in taste buds to detect taste
2. enantiomers can interact differently with chiral receptor cells in the nose to detect smell
3. drugs work by interacting with the appropriate receptor site via IMF which are very specific