Aldehydes, Ketones, and IR spec

Question 1

What are the 2 ways aldehydes can be synthesised?

Answer 1

• Hydroformylation which involves the addition of a formyl group and a H atom to a C-C double bond
• Primary Alcohol oxidation

Question 2

What suffix is added when the CHO functional group is attached to a ring?

Answer 2

Carbaldehyde

Question 3

What are the physcial properties of aldehydes?

Answer 3

1. Diverse properties that depend on the remainder of the molecule
2. H atom attached to carbonyl makes aldehydes easy to oxidise
3. C of C=O susceptible to nucleophilic attack
4. Can act as a H-bond acceptor

Question 4

How are ketones synthesised?

Answer 4

• Oxidation of secondary alcohols
• Hydration of alkynes
• Friedel-Crafts acylation (for aromatic ketones)

Question 5

What are is the shape and bond angles of ketones?

Answer 5

Trigonal planar around ketonic carbon and angles of 120°

Question 6

What are the physical properties of ketones?

Answer 6

• C of C=O group is susceptible to nucleophilic attack
• Can act as a H-bond acceptor but not a H-bond donor

Question 7

Is the carbonyl group electronegative?

Answer 7

Yes

Question 8

How can the carbonyl group be tested for?

What happens if the result is positive?

Answer 8

• 2,4-DNPH (Brady’s reagent) is added
• Yellow-orange precipitate is produced

Question 9

What is used to test for the prescence of an aldehyde? What gives a positive test?

Answer 9

• Tollens’ reagent
• Silver mirror is formed

Question 10

What affects the wavelength at which a specific bond absorbs IR light?

Answer 10

its chemical environment

Question 11

How does IR spec work?

Answer 11

Uses electromagnetic radiation in the IR region of the EM spectrum as a source of energy to power the vibration of covalent bonds in a compound

Question 12

What is the relationship between mass and frequency of bond vibration?

Answer 12

The lower the mass the higher the frequency of bond vibration

Question 13

What is the relationship between bond strength and speed of bind vibration?

Answer 13

Strong high energy binds have a high vibration frequency whilst weak low energy bonds have a low vibration frequency

Question 14

What influences the speed of bond vibration?

Answer 14

1. The strength of the bond joining two atoms
2. The combined mass of the joined atoms

Question 15

Give 5 different ways bonds can vibrate

Answer 15

• Stretch
• Scissor
• Rock
• Wag
• Twist

Question 16

What phenomenon does IR spec exploit?

Answer 16

The differing vibrations of covalent bonds

Question 17

Give 2 groups which are H bond donors

Answer 17

• 1° amine
• Hydroxyl

Question 18

Give 3 groups which are H bond acceptors

Answer 18

• Carbonyl
• Hydroxyl
• 3° amine