Aldehydes and Ketones

Question 1

Aldehydes Outline

Answer 1

C attached to an O with a double bond, a H and either another H/C

Question 2

Ketone Outline

Answer 2

C attached to an with a double bond and 2 other substituents (but not H)

Question 3

Carbonyl C Outline

Answer 3

C attached to 3 substituents (1 double bonded). Triagonal planar. 120 degrees between substituents

Question 4

Relationship between C and O

Answer 4

O is more electronegative then C. O = delta negative, C = delta positive

Question 5

Alpha C Outline

Answer 5

C attached to carbonyl C. One of the H’s on alpha C is acidic (electrons drawn to delta positive C). H+ is ionised

Question 6

Which is more reactive an aldehyde or a ketone

Answer 6

aldehyde. Due to the fact that ketone substituents are more complex. Ketones carbonyl C is less electrophilic the aldehydes as it has more electron pushing substituents

Question 7

What increases the electrophilicity of the carbonyl C

Answer 7

Acid catalyst (makes C more delta positive)

Question 8

What increases the nucleopholicity of the carbonyl C

Answer 8

Alkaline catalyst (makes O more delta negative)

Question 9

Hemiacetal Outline

Answer 9

1 ether and 1 alcohol on the same C . Aldehyde/ketone + alcohol (steriochemic amount) with acidic catalyst

Question 10

Acetal Outline

Answer 10

Acetal has 2 ether functional groups. Hemiacetal in presence of acididc catalyst

Question 11

Hemiacetal Formation Outline

Answer 11

protonation of carbonyl group, nucleophilic addition of alcohol, hemiacetal formation and catalyst regeneration

Question 12

Carbonyl group protonation Outline

Answer 12

H+ ion adds to ketone/aldehyde. Forms a resonsnce structure alternating between a C O double bond (positive O, C is more strongly electrophilic) and a C O single bond (positive C)

Question 13

Addition of an alcohol Outline

Answer 13

OH ion adds to resonsnce structure. OH group O becomes positively charged (rest of molecule is nuetral). Rate limiting (slowest step)

Question 14

Formation of hemiacetal and regeneration of catalyst

Answer 14

To neutralise O, H donates an electron severing bond to O forming H+ ion. Resulting in a neutral hemiacetal molecule

Question 15

What is notable about hemiacetal formation

Answer 15

All steps are reversible

Question 16

Hemiacetal to Acetal Outline

Answer 16

Reacting an alcohol with a hemiacetal in the presence of an acidic catalyst. Add a substituent to hemiacetal (without H). Forms acetal and water

Question 17

What is the most stable hemiacetal

Answer 17

6 membered ring

Question 18

What changes when sugar is converted to hemiacetal

Answer 18

Structure. Triagonal planar C to Tetrahedral C

Question 19

Condensation Reaction Def

Answer 19

addition reaction followed by elimination of water

Question 20

Imine Outline

Answer 20

Reagent in acetal formation is an amine (originally attached to alcohol)

Question 21

Oxime Outline

Answer 21

Reagent in acetal formation is hydroxylamine (OH attached to alcohol)

Question 22

Hydrazone Outline

Answer 22

Reagent in acetal formation is hydrazine (NHR)

Question 23

Which is a better nucleophile N or O

Answer 23

N is the more nucleophilic. While it has 1 less lone electron then O, it is less electronegative (less stable = more reactive)

Question 24

Which is a better nucleophile NH and NH2

Answer 24

NH2. Due to NH being an electron withdrawing group, NH is more stable

Question 25

Example of a poor leaving group

Answer 25

OH

Question 26

Example of a good leaving group

Answer 26

H2O

Question 27

How does a H neutralise the charged atom it's attached to

Answer 27

Donate both electrons in bond to charged atom. Bond is severed, atom has new lone pair (neutralised) and H+ ion is formed (reformed catalyst/ substance to nuetralise a negatively charged atom)