Reactions of Haloalkanes

Question 1

nucleophilic substitution reaction

Answer 1

haloalkanes- substrate and the nucleophile attacks the substrate and a halide ion departs.

Question 2

what are ambident nucleophiles?

Answer 2

nucleophiles having two nucleophilic centers. like cyanide(CN) and nitrite ion(NO2)

Question 3

what compounds does cyanide produce?

Answer 3

through carbon atom- alkyl cyanide
through nitrogen atom-isocyanides

Question 4

Sn2 mechanism explanation

Answer 4

new carbon-nucleophile formation and breakage of carbon-halogen bond takes place simultaneously. primary halides react rapidly in sn2 reactions as they are no bulky substituents hindering the approaching nucleophiles.

Question 5

sn2 reaction order of reactivity

Answer 5

primary>secondary>tertiary

Question 6

sn1 mechanism explanation

Answer 6

occurs in two steps
1. cleavage of C-Br bond to produce a carbocation and bromide ion(slow and reversible)
2.attack of nucleophile on carbocation to complete the substitution reaction.

Question 7

how is energy for sn1 reaction obtained

Answer 7

solvation of halide ion in protic solvents like water, alcohol and acetic acid.

Question 8

why does tertiary undergo sn1 easily?

Answer 8

due to its more stable carbocation, the rate of reaction will be faster.

Question 9

order of reactivity of sn1 reaction

Answer 9

3>2>1

Question 10

allylic and benzylic halides show high reactivity towards sn1 or sn2 and how does carbocation get stabilised

Answer 10

sn1 and carbocation gets stabilised by resonance.

Question 11

optical activity

Answer 11

compounds can rotate a plane of optical light

Question 12

dextrorotatory (+)

Answer 12

light is rotated clockwise(to the right)

Question 13

laevo-rotatory (-)

Answer 13

light is rotated anticlockwise.

Question 14

what is configuration

Answer 14

spatial arrangement of functional groups around carbon.

Question 15

asymmetric carbon

Answer 15

substituents are all different and the mirror image is not superimposed(overlap)

Question 16

chirality

Answer 16

compounds which are non-superimposable on their mirror image

Question 17

are chiral objects optically active

Answer 17

yes

Question 18

examples of chiral molecules

Answer 18

butan-2-ol, 2-chlorobutane, 2,3-dihydroxypropanal

Question 19

what are enantiomers?

Answer 19

the stereoisomers related to each other has non-superimposable mirror images are enantiomers.

Question 20

Nature of enantiomers

Answer 20

identical physical properties like melting, boiling point and refractive index

Question 21

Racemic mixture

Answer 21

A mixture containing two enantiomers in equal proportions having zero optical rotation as it gets cancelled by each other.

Question 22

Racemisation

Answer 22

Conversion of an enantiomer into a racemic mixture

Question 23

Retention

Answer 23

the spatial arrangement of bonds does not change after a reaction but the signs may change.

Question 24

sn2 reactions of optically active halides are accompanied by

Answer 24

inversion of configuration

Question 25

what happens in sn1 reactions of optically active hlides

Answer 25

carbocation formed in step 1 is achiral so the nucleophile can attack on both sides resulting in a mixture by a process of racemisation.

Question 26

elimination reaction

Answer 26

base reacts with a haloalkane to form an alkene as a hydrogen atom is eliminated from B carbon and halogen is elimination from Alpha carbon

Question 27

Zaitsev’s Rule

Answer 27

The preferred product is the alkene having more alkyl groups attached to the double bonded carbon atoms in the dehydrohalogenation reaction.

Question 28

how are Grignard reagents formed?

Answer 28

Reaction of haloalkanes with magnesium in dry ethr.

Question 29

Why are grignard reagents kept away from moisture

Answer 29

as it will form hydrocarbons

Question 30

wurtz reaction

Answer 30

haloalkane + Na to give RR + NaX