hydroxyl compounds

Question 1

why are alcohols weaker acids than water

Answer 1

1. alkyl groups are inductively electron-donating and will intensify the negative charge on the alkoide ion, which has a greater tendency as compared to the hydroxide ion to accept a proton to re-form the alcohol molecule
2. the alkoxide is said to be destabilised

Question 2

why are phenols stronger acids than water

Answer 2

1. the p orbital of the negatively charged oxygen is able to voerlap with the pi eectron cloud of the benzene ring
2. the negative charge is able to delocalise into the benzene ring to some extent, and the pheonxide ion is stabilised to a larger extent than the alkoxide ion

Question 3

reagents, conditions and observations for acid metal reaction with sodium

Answer 3

1. reagents and conditions: sodium metal, RTP
2. observations: slow effervescence of hydrogen gas in alcohols, rapid effervescence of hydrogen gas in phenols

Question 4

reagents, conditions and observations for acid base reaction with sodium hydroxide

Answer 4

1. reagents and conditions: sodium hydroxide, RTP
2. observations: cloudy mixture dissolves to form colourless homogenous solution

Question 5

reagents, conditions and observations for nucleophilic substitution with phosphorus V chloride

Answer 5

1. reagents and conditions: PCl5
2. observations: dense white fumes of HCl produced

Question 6

reagents, conditions and observations for nucleophilic substitution with phosphorus trihalides

Answer 6

1. reagents and conditions: PCl3, RTP or P, Br2, heat or P, I2, heat
2. PBr3 and PI3 are prepared in situ by heating red phosphorus with bromine and iodine respectively

Question 7

reagents, conditions and observations for nucleophilic substitution with hydrogen chloride

Answer 7

1. reagents and conditions: concentrated HCl for tertiary alcohols, concentrated HCl, ZnCl2 catalyst and heat for primary or secondary alcohols
2. observations: solution turns cloudy

Question 8

reagents, conditions and observations for nucleophilic substitution with hydrogen bromide

Answer 8

1. reagents and conditions: concentrated HBr, concentrated H2SO4, heat

Question 9

reagents, conditions and observations for nucleophilic substitution with hydrogen iodide

Answer 9

1. reagents and conditions: concentrated HI

Question 10

reagents, conditions and observations for nucleophilic substitution with thionyl chloride

Answer 10

1. reagents and conditions: SOCl2, warm
2. observations: SO2 gas and white fumes of HCl produced

Question 11

reagents, conditions and observations for dehydration of alcohols

Answer 11

1. reagents and conditions: concentrated H3PO4 catalyst, heat or exccess concentrated H2SO4, heat or Al2O3, heat
2. H3PO4 is preferred over H2SO4 as the latter may act as an oxidising agent, produced uwanted side products
3. only alcohols with at least one H atom on the C atom adjacent to the C atom bearing the hydroxy group can undergo dehydration

Question 12

reagents, conditions and observations for condensation with carboxylic acids

Answer 12

1. reagents and conditions: alcohol, carboxylic acid, few drops of concentrated H2SO4, heat
2. reaction is slow and reversible

Question 13

reagents, conditions and observations for condensation with acyl chlorides

Answer 13

1. reagents and conditions: acyl chloride, alcohol or phenol, RTP
2. observations: white fumes of HCl produced
3. reaction goes to completion

Question 14

why does the condensation reaction between the phenol and the acyl chloride have better yield when the reaction is carried out under basic conditions

Answer 14

1. the basicity of the solution allows for the phenoxide ion to first generate
2. the negative charge of the phenoxide ion increases the electron density around the O atom, making it a stronger nucleophile than phenol

Question 15

reagents, conditions and observations for oxidation of primary alcohols to aldehydes

Answer 15

1. reagents and conditions: K2Cr2O7, H2SO4, heat with immediate distillation
2. observations: orange solution turns green

Question 16

reagents, conditions and observations for oxidation of primary alcohols to carboxylic acids

Answer 16

1. reagents and conditions: K2Cr2O7, H2SO4, heat under reflux or KMnO4, H2SO4, heat under reflux
2. orange solution turns green or purple solution turns colourless

Question 17

reagents, conditions and observations for oxidation of secondary alcohols to ketones

Answer 17

1. reagents and conditions: K2Cr2O7, H2SO4, heat under reflux or KMnO4, H2SO4, heat under reflux
2. orange solution turns green or purple solution turns colourless

Question 18

reagents, conditions and observations for the iodoform test, to deduce the presence of a CH3CHOH group in an alcohol

Answer 18

1. reagents and conditions: I2, NaOH, warm
2. observations: yellow ppt is formed
3. this reaction involves the breaking of a C-C bond with the removal of a methyl group, and is useful in shortening a carbon chain]

Question 19

reagents, conditions and observations for electrophilic substitution with nitric acid with phenol

Answer 19

1. reagents and conditions: dilute HNO3 or concentration HNO3
2. observation: pale yellow liquid formed

Question 20

reagents, conditions and observations for electrophilic substitution with bromine with phenol

Answer 20

1. reagents and conditions: aqueous Br2, RTP or liquid Br2
2. observations: yellow-orange solution decolourised, white ppt formed or reddish-brown liquid decolourised, white fumes of HBr evolved

Question 21

reagents, conditions and observations for complex formation with iron (III) chloride

Answer 21

1. reagents and conditions: neutral FeCl3, RTP
2. observations: violet colouration