carbonyl chemistry

Question 1

is the carbonyl bond polar and why?

Answer 1

Yes- oxygen is more electronegative than carbon
the carbon is electron deficient and susceptible to attack
Oxygen is electron rich and can react with electrophile

Question 2

shape and bond angle of carbonyl

Answer 2

trigonal planar 120degrees

sp2

Question 3

what is the reactivity of the carbonyl bond?

Answer 3

undergo nucleophilic and electrophilic addition

Question 4

why are aliphatic aldehydes more reactive than aromatic?

Answer 4

aromatic are less reactive as somatic ring delocalises the positive charge away from the carbonyl carbon

Question 5

Basic conditions of carbonyl

Answer 5

NaOH, H20

Nucleophile (OH-) will attack bond

Question 6

acidic conditions

Answer 6

carbonyl bond (O) attacks the H+ to form a conjugate acid
Nu attach onto the conjugate acid, loss of H from NU forming the product

Question 7

Draw the mechanisms for acidic and basic conditions of carbonyl mechanisms

Answer 7

..

Question 8

What nucleophiles are there that can participate in carbonyl addition?

Answer 8

oxygen (alcohol addition to aldehyde or ketone) produces a hemiactal, usually acid catalysed

sulfur - reaction of thiols is the same as the alcohols. reaction with thiol more favourable due to increased nucleophilicity

hydride - carbonyl of the aldehyde or ketone can be reduced to an alcohol using hayride. Usually LiAlH4 or NaBH4

carbon - cyanide (HCN) produces cyanohydrins
Grignard
acetylides - treatment of a terminal acetylene with strong base produces acetylides

Question 9

What does oxygen as a nucleophile do?

Answer 9

addition of alcohol to aldehyde or ketone produces a hemiacetal
ACID CATALYSED

Question 10

in the reaction of oxygen as a nucleophile - is it reversible?

Answer 10

Yes- base catalyse it using OH - attach of the product

Question 11

what can stabilise the hemiacetal to drive the equilibrium in its favour?

Answer 11

cyclic products arising from an intramolecular reaction

Question 12

what does adding a further equivalent of an alcohol to a haemiacetal do?

Answer 12

forms an acetal - acid catalysed only

Question 13

the reaction of thiols (sulfur Nu) and Oxygen as a Nu with aldehydes and ketones is the same - so which is more favourable?

Answer 13

reaction with thiols more favourable due to increased nucleophilicity
produces hemithioacetal and then with further reaction produces thioacetal

Question 14

what does hydride addition (LiALH4) to aldehyde or ketone produce?

Answer 14

alcohol -reduction reaction

Question 15

what is formed when nitrogen acts as a nucleophile attacking aldehydes/ketones?

Answer 15

amine attack (nitrogen) forms imines 
NH2

Question 16

what is imine reactivity?

Answer 16

they are nitrogen analogues of carbonyl groups

the C=N behaves as C=O

Question 17

Give examples of good leaving groups

Answer 17

acyl halides RCOX e.g Cl-, Br-
Thioacids RCOSH e.g HS-
Thioesters e.g RCOSR e.g RS-
Anhydrides (RCO)2 - RCO2-

Question 18

Examples of moderate LGs

Answer 18

acids RCO2H - H20 (OH-)
esters RCO2R - ROH (RO-)
amides RCOHN2 - NH3 (NH2-) or R2NH

Question 19

Examples of poor LGs

Answer 19

aldehydes RCHO - H-

Ketones RCOR - R-

Question 20

How are esters formed?

Answer 20

acid + alcohol –> ester + water

also prepared more conveniently by using more reactive carbonyl derivatives - acyl halides and anhydrides