4.1 Organic Chemistry III

Question 1

type of isomerism

name 2

Answer 1

structural isomers

stereoisomers

Question 2

structural isomers

meaning

Answer 2

same molecular formula

different structural formula

Question 3

stereoisomers

meaning

Answer 3

same structural formula

different arrangement of groups in space

Question 4

stereoisomers

two types and its explanation

Answer 4

geometrical / E/Z ( cis-trans ) isomers
- groups fixed in different space as a result of the restricted rotation of double bonds

optical isomers

• groups fixed in different space as a result of the asymmetry of the structure
• non - superimposable mirror images of each other

Question 5

isomerism

occurs when?

Answer 5

two or more compounds have the same molecular formula but different arrangement of the atoms in the molecules

Question 6

three types of structural isomerism

Answer 6

chain isomers

positional isomers

functional group isomers

Question 7

geometrical isomerism

is due to?

Answer 7

restriction rotation of the carbon = carbon double bond

both C atoms of C=C must have different groups / atom

Question 8

cis isomers

Answer 8

same side of the double bond

Question 9

trans isomers

Answer 9

opposite sides of the double bond

Question 10

draw skeletal formula of trans but - 2 - ene

Answer 10

like a chair

refer notes on pg 17 at 1.6

Question 11

draw skeleton formula of cis but - 2- ene

Answer 11

like a bowl

refer notes on pg 17 at 1.6

Question 12

geometrical isomers

E/Z isomers – if both C OF C= C have 2 different groups attached

E?
Z?

Answer 12

E
highest priority opposite sides

Z
highest priority together

the higher the atomic number of the atom/group attached to C=C , the higher its priority

Question 13

optical isomers compounds have

carbon at the centre is called chiral centre

2 characteristics

Answer 13

• 4 different atoms or groups ( asymmetrical carbon atom )

- mirror image is non superimposable ( chirality )

Question 14

stereoisomers

Answer 14

molecules of organic compound with the same structural formula but different arrangement of the atoms in space

Question 15

chiral carbon

Answer 15

is the atom in a molecule which is attracted to 4 diff atoms / group of atoms

Question 16

chiral atom / centre

Answer 16

is the carbon atom

in a molecule which is attracted to 4 diff atoms / group of atoms

Question 17

chiral molecule

Answer 17

a molecule which has an isomer that is a mirror image of itself

the two being non - superimposable

Question 18

optical isomers

enantiomers

Answer 18

non superimposable mirror image of each other

Question 19

optical isomers have identical physical and chemical properties

they differ in two ways

Answer 19

• optical isomers are optically active
  > they rotate the plane of polarised light in opposite direction
• optical isomers have diff biochemical reactions

Question 20

why an equimolar mixture does not rotate light at all?

Answer 20

one isomer rotates slight to the left, the other to the left

opposite and equal rotations cancel

this optically inactive mixture is called racemic mixture / racemate

Question 21

how optical activity detected experimentally

Answer 21

when a beam of plane polarised light ( monochromatic
) passes through a solution of single optical isomer

the plane of polarisation rotates

Question 22

In SN1 mechanism
the product is optically inactive because racemic mixture of the two optical isomers are produced

draw the mechanism

Answer 22

refer notes pg 6

Question 23

In SN2 mechanism
the product will rotate the plane of polarised light

draw the mechanism

Answer 23

refer notes pg7