ch 6 - Aldehydes and Ketones 1: Electrophilicity and Oxidation-Reduction

Question 1

carbonyl

Answer 1

double bond between a carbon and an oxygen

Question 2

ketone

Answer 2

two alkyl groups bonded to the carbonyl; never terminal

Question 3

aldehyde

Answer 3

one alkyl group bonded to carbonyl and one hydrogen; always terminal

Question 4

naming aldehydes

Answer 4

replace -e at the end of alkane name with suffix -al; as substituent, use prefix oxo-; if attached to ring suffix -carbaldehyde is used

Question 5

naming of ketones

Answer 5

replace -e of alkane with suffix -one. when naming common names, two alkyl groups are named alphabetically followed by -ketone. as substituents, use prefix oxo- or keto-

Question 6

boiling point of ketones and aldehydes

Answer 6

higher than parent alkanes because dipole moments associated with polar carbonyl groups increase intermolecular attractions but less than alcohols because no hydrogen bonding is present in these

Question 7

reactivity of aldehydes and ketones

Answer 7

double bond to oxygen causes these to be more electron-withdrawing than alcohols; act as electrophiles (targets for nucleophiles) which leaves a partial positive charge on the carbon; aldehydes are generally more reactive toward nucleophiles because of less steric hindrance and few electron-donating alkyl groups

Question 8

formation of aldehyde from primary alcohol

Answer 8

PCC the only means by which a primary alcohol is partially oxidized to an aldehyde; with stronger oxidants, aldehydes will continue to carboxylic acids

Question 9

ketone from secondary alcohol

Answer 9

any strong oxidant: Na2Cr2O7, K2Cr2O7, CrO3, PCC; reaction stops at the ketone stage and does not oxidize further

Question 10

geminal diols

Answer 10

aldehydes and ketones react with water to form this (1,1 diols): nucleophilic oxygen in water attacks the electrophilic carbonyl carbon; can increase rate by adding small amount of catalytic acid or base

Question 11

formation of hemiacetal or hemiketal

Answer 11

aldehyde/ketone reacted with one equivalent of alcohol (nucleophile in this reaction), hemiacetal or hemiketal results, respectively; marked by retention of hydroxyl group (end point in basic conditions)

Question 12

formation of acetals and ketals

Answer 12

result from two equivalents being added to aldehydes and ketones respectively. proceeds by nucleophilic substitution reaction (SN1) and is catalyzed by anhydrous acid; these are used as protecting groups and can easily be reversed by aqueous acid and heat

Question 13

formation of imine

Answer 13

nitrogen and nitrogen-based functional groups act as good nucleophiles because of lone pair on nitrogen; this results from ammonia reacted with aldehyde or ketone; it is a nitrogen atom double-bonded to a carbon atom; is a condensation reaction and an example of nucleophilic substitution

Question 14

condensation reaction

Answer 14

reaction in which a small molecule is lost during the formation of a bond between two molecules (ex is formation of imines)

Question 15

common ammonia derivative molecules that react with aldehydes and ketones

Answer 15

ammonia (NH3) and its derivatives, hydroxylamine (N2H-OH), hydrazine (H2N-NH2), semicarbazide (H2N-NH-C(O)NH2) forming oximes, hydrazones, and semicarbazones respectively

Question 16

enamines

Answer 16

formed from tautomerization of imines and related compounds

Question 17

formation of cyanohydrins

Answer 17

aldehydes/ketones reacted with HCN (cyanide) which has both triple bonds and an electronegative nitrogen atom; after hydrogen dissociates, nucleophilic cyanide anion can attack the carbonyl carbon atom. this is the result once the oxygen has been reprotonated; has stability from the newly formed C-C bond

Question 18

oxidation of aldehydes to carboxylic acids

Answer 18

CH3C(double bond O)H + either one of these: KMnO4, CrO3, Ag2O, H2O2 -> CH3 C(double bond O) OH (a carboxylic acid) [note that ketones cannot be oxidized more because they are already as oxidized as a secondary carbon can get.

Question 19

reduction of aldehydes and ketones to alcohols

Answer 19

often performed with hydride reagents: most commonly lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4)