Carbonyl compounds

Question 0

Ketone

Answer 0

• COC-

eg. ButanONE

Question 1

Aldehyde

Answer 1

-CHO

eg butenAL

Question 2

Alkyl

Answer 2

Alkane with H atom removed

Question 3

Aryl

Answer 3

Cyclic compound containing benzene ring

Question 4

Why is carbonyl group polar?

Answer 4

C=O bond polar due to electronegativity on oxygen atom - more electrons in bond (Pi and sigma) towards O atom

Question 5

Why is C=O soluble in water?

Answer 5

Polar so smaller aldehydes and ketones are soluble in water - form H bonds (up to 4 carbons in the chain)

Question 6

Why do ketones and aldehydes has higher boiling points than alkanes?

Answer 6

Permanent dipole-dipole forces between molecules

Question 7

What is the oxidising agent used in the oxidation of alcohols and aldehydes?

Answer 7

[O] = Potassium dichromate (VI) with sulfuric acid or acidified potassium dichromate (Cr3O72-) which is orange and goes to green Cr3+

Question 8

Conditions for primary alcohol ➡️ Aldehyde and ?

Answer 8

Heat gently and distill using oxidising agent

Forms 1 molecule of water too

Question 9

Conditions for oxidisation of ketone to carboxylic acid and ?

Answer 9

Heat under reflux with excess H2SO4 and oxidising agent
1 molecule of water also forms

Cannot be oxidising further

Question 10

Condistions for secondary alcohol ➡️ ketone

Answer 10

Heat gently using oxidising agent
Forms 1 molecule of water too

Cannot be oxidised further and tertiary alcohols cannot be oxidised at all

Question 11

Reducing agent for reduction of carbonyl compounds

Answer 11

2[R] = ️sodium tetrahydridborate (III), NaBH4, which is a source of H-

Question 12

Conditions for reduction of aldehydes ➡️ primary alcohols and ketones ➡️ secondary alcohols

Answer 12

Warm using reducing agent and water as the solvent

Question 13

Mechanism for reduction of carbonyl compounds

Answer 13

Nucleophilic addition
1) nucleophilic attack H- with lone pair to Cdelta+ and pair of electrons from Pi bond to Odelta-
2) adding water - lone pair on O- goes to H atom on water and pair of electrons in H-O bond goes to the O
Forms an alcohol and OH- molecule

Question 14

Brady’s reagent test

Answer 14

2,4-dinitrophenylhydrazine
Addiction across a double bond and elimination of water means ghat a C=O bond is present
Forms a yellow/orange precipitate with only aldehydes and ketones
To find specific ketone or aldehyde, the mpt of the crystals formed can be compared with a database

Question 15

Silver mirror test

Answer 15

Tollens’ reagent - ammonical silver nitrate [Ag(NH3)2]+
Add tollens’ reagent and warm gently in a water bath
A silver mirror forms on the side of the test tube from a colourless solution with aldehydes only
The aldehyde is oxidised and Ag+ reduced
No silver mirror with ketones as cannot be oxidised further

Question 16

Carboxylic acids

Answer 16

-COOH

Question 17

Why do carboxylic acids partially dissociate?

Answer 17

Weak acids

Question 18

Why are carboxylic acids soluble in water?

Answer 18

Highly polar - C=O and O-H
Form H bonds - 2 per molecule
Only soluble up to 4 C in chain length as longer chain non-polar

Question 19

Carboxylic acid + metal ➡️

Answer 19

Metal salt + H2

Question 20

Carboxylic acid + carbonate

Answer 20

Metal salt + CO2 + H2O

Question 21

Carboxylic acid + base ➡️

Answer 21

metal salt + water

Question 22

Esters

Answer 22

-COOC
From carboxylic acid and alcohol
Name alcohol then acid eg ethyl propanoate

Question 23

Formation with carboxylic acid and alcohol

Answer 23

With conc H2SO4 catalyst

Goes to ester and water

Question 24

Formation from acid anhydride and alcohol

Answer 24

Acid anhydride - 2 carboxylic acids with water molecule removed
React with alcohol - forms ester (usual naming - alcohol then acid) and a carboxylic acid
Forms a better yield of ester as not reversible

Question 25

Uses of esters

Answer 25

Perfumes
Food flavourings
Oils

Question 26

Acid hydrolysis of esters

Answer 26

Reflux ester with dilute H2SO4 or HCl

Ester + water (reversible) ➡️ carboxylic acid and alcohol

Question 27

Alkali hydrolysis of esters

Answer 27

Reflux with alkali eg NaOH

Ester + NaOH ➡️ metal salt + alcohol

Question 28

What is a triglyceride?

Answer 28

• a triester of propane-1,2,3-triol (glycerol) and a fatty acid (octadecanoic or hexadecanoic acid). All 3 alcohol groups esterified

Question 29

What does C18,1(9) mean?

Answer 29

18 carbons, 1 double bond on the 9th carbon of a fatty acid (carboxylic acid)
There are trans and cis versions of this

Question 30

Why are saturated and trans fatty acids worse for health?

Answer 30

Pack together more closely a solid and block arteries leading to CHD and increased heart attack risk
Contain bad LDL cholesterol which sticks to artery walls and plaque builds up

Question 31

Why are monounsaturated and polyunsaturated fatty acids better for health?

Answer 31

Contain good HLD (high lipo-density) cholesterol which carries bad cholesterol away from arteries so lower blood pressure and lower risk of CHD

Question 32

What is biodiesel made from?

Answer 32

Vegetable oil or animal fat - long chain alkyl esters

Triglyceride + 3H3OH (reversible + NaOH) ➡️ 3H3C-O-C=O + glycerol

Question 33

What is biodiesel used in and what are the issues?

Answer 33

Used in standard Diesel engines or blended with petrodiesel
Carbon neutral: same amount of CO2 absorbed when growing as is released when burned as a fuel
But may lead to increase in food prices and starvation