Aldehydes and Ketones

Question 1

What are primary and secondary alcohols oxidised to

Answer 1

aldehydes and ketones

Question 2

what are aldehydes and ketones reduced to with NaBH4

Answer 2

primary and secondary alcohols

Question 3

what is the oxidising agent for primary and secondary alcohols to be oxidised into aldehydes and ketones

Answer 3

acidified potassium dichromate (VI)

Question 4

what is the reducing agent for aldehydes and ketones to be reduced into primary and secondary alcohols

Answer 4

aqueous NaBH4

Question 5

what happens in reduction of aldehydes and ketones with NaBH4

Answer 5

2 Hydrogen atoms are added to the carbon and to the oxygen

Question 6

what are aldehydes reduced to

Answer 6

primary alcohols

Question 7

what are ketones reduced to

Answer 7

secondary alcohols

Question 8

what is a nucleophile

Answer 8

an electron pair donor

Question 9

why can the C=O bond in aldehydes and ketones be attacked by nucleophiles

Answer 9

because it is a polar bond

Question 10

what is a polar bond

Answer 10

a polar bond is the unequal distribution of electrons in a covalent bond because of a difference in electronegativity between atoms

Question 11

what mechanism is used in the reduction of aldehydes and ketones to primary and secondary alcohols

Answer 11

nucleophillic addition

Question 12

what is the reducing agent to form primary and secondary alcohol

what does the reducing agent for aldehydes and ketones provide in the nucleophillic addition mechanism

Answer 12

NaBH4
a hydride ion :H- (nucleophile) and it attacks the delta positive carbon

Question 13

what mechanism is it when aldehydes and ketones react with potassium cyanide (KCN) and dilute HCl

what actually occurs in this mechanism

Answer 13

nucleophillic addition

reduction of aldehydes and ketones into hydroxynitriles

Question 14

what has priority in the carbon chain - the hydroxy or nitrile

Answer 14

the nitrile

Question 15

what is the nucleophile in nucleophillic addition mechanism to form hydroxynitriles

Answer 15

:CN-

from potassium cyanide

Question 16

where does the proton H+ come from in the 2nd step for production of hydroxynitriles

Answer 16

the dilute acid (HCl)

Question 17

what is the problem about KCN

what happens when KCN reacts with water

where should this experiment take place

Answer 17

it is an irritant and toxic when eaten

Hydrogen cyanide is produced which is a highly toxic gas

in a fume cupboard with glasses labcoat gloves

Question 18

which group of isomers do optical isomers belong to

Answer 18

stereoisomers

Question 19

what do all optical isomers contain

Answer 19

a chiral centre

Question 20

what is a chiral centre

Answer 20

a single carbon atom bonded to 4 different atoms or groups

Question 21

what is the word when optical isomers cannot be placed on top of its mirror image as they are different

Answer 21

non-superimposable

like a pair of hands

Question 22

optical isomers have no:

Answer 22

no centre of symmetry
no plane of symmetry
no axis of symmetry

Question 23

what is another word for optical isomers

Answer 23

enantiomers

Question 24

what are the similarities of a pair of optical isomers

what are the differences

Answer 24

same physical and chemical properties

they rotate the plane of polarised light in opposite directions

Question 25

how do light waves normally travel?

Answer 25

normally light waves vibrate in all directions perpendicular to the direction of travel

Question 26

how do we make plane polarised light ?

Answer 26

when we pass the light through a polarising filter, only waves vibrating in one direction are allowed through

resulting in plane polarised light

Question 27

what happens when this new plane of polarised light passes through a solution of an enantiomer

Answer 27

the plane gets rotated through a particular angle

essentially different enantiomers of the same sample rotate the plane differently

Question 28

explain the differences on how enantiomers of the same sample rotate the plane

Answer 28

one enantiomers will rotate the plane polarised light in the left (anticlockwise) direction. it is also called laevorotary or (-) direction

the other enantiomer rotates the plane of light in the right (clockwise) direction. it is also called the dextrorotary direction or (+) direction

Question 29

what happens to the rotation of light when there’s only one form of the optical isomer in the sample

and what is the sample called

Answer 29

when the sample only contains one form of the optical isomer then the plane of polarised light will be rotated in one direction

the sample is said to be optically active

Question 30

what is a racemic mixture

Answer 30

when the sample contains both optical isomers in equal quantities so is optically inactive as 2 enantiomers rotate the plane of polarised light in opposite directions equally

Question 31

what happens when both optical isomers in equal quantities are present in the sample

and what is the sample said to be

Answer 31

there will be no observation of the plane polarised light rotating

optically inactive

Question 32

what is another word for clockwise

Answer 32

dextorotary direction

Question 33

what’s another word for anticlockwise

Answer 33

laevatorotary direction

Question 34

explain the formation of optical isomers from aldehydes and ketones

Answer 34

1) the carbonyl group is planar

2) this means the nucleophile has an equal chance of attacking from either side

3) a racemic mixture is formed