carbonyl electrophile

Question 1

what is burgi-Dunitz angle

Answer 1

the angle between incoming Nu (pi* location) and C=O bond at 107*

Question 2

what is the difference between nucleophilic attack of aldehyde and ketone

Answer 2

aldehyde faster as additional group on ketone hinders attack by steric and also via electronic, sigma conjugation as donation of e from sigma C-H bond into pi* of C=O causes the H of ketone group to become acidic

Question 3

how can ketone act a bronsted base

Answer 3

sigma C-H and pi*C=O overlap making C-H acidic,, so when hindered ketone reacts with hindered nu deprotonation on carbonyl more likely than Nu attack.

Question 4

how are cyanohydrins formed and reversed

Answer 4

ketone or aldehyde reacted with HCN where CN- is added across C=O bond.
can be reversed: with NaOH giving carbonyl NaCN and H2O
equilibrium position depends on structure Keq larger for aldehyde

Question 5

how are hydrates formed and reversed

Answer 5

by adding or removing H2O across the C=O bond

Question 6

how are hemiacetals formed

Answer 6

addition of alcohol to carbonyl catalysed by acid and by base , more convenient with an acid

cyclic hemiacetals can be formed by intramolecular addition of hydroxy groups to carbonyl groups

Question 7

how are alcohols formed from aldehydes

Answer 7

react aldehyde with NaBH4 in CH3OH giving primary alcohol

Question 8

how are alcohols formed from ketone

Answer 8

react with LiAlH4 in O(C2H5)2 with H2O work up forming secndary

Question 9

what is the trend in bond order going from acyl chloride -> acid anhydride -> ester -> amide

Answer 9

C-O bond order decreases as increase lone pair interaction from X into pi* of C=O
Going in opposite direction increase in nc=o -> sigma*c-x increasing C-O bond order LP on O into antibonding orbitals of C-Cl

Question 10

how does reactivity of carboxylic derivatives link to IR spec trends

Answer 10

As IR peak decreases, nx -> pi*c=o increases:
C-O bond order decreases
reduce reactivity towards nu
increase reactivity toward electrophiles

Question 11

what is correlation between LG of carboxylic derivative l pKa of conjugate acid and reactivity towards Nu

Answer 11

Negative correlation as pKa increases reactivity towards Nu decreases
pKa HCl = -7
RCO2H = 5
ROH = 17-19
R2NH = 35