alcohols

Question 1

Describe the polarity of alcohols using the idea of electronegativity and bond dipoles

Answer 1

oxygen has a higher electronegativity than H
electrons in bond closer to the O atom and so O-H bond is polar

Question 2

explain the relatively low volatility of alcohols compared with alkanes using the idea of H bonding

Answer 2

-alkanes strongest IMF is induced dipole dipole forces, which are relatively weak and don’t require much energy to break
-alcohols strongest IMF is H bonding (also have permanent and induced)
- H bonding between water molecules is stronger than the induced dipole interactions in alkanes and therefore requires more energy to overcome, less volatile

Question 3

primary, secondary and tertiary alcohols

Answer 3

-primary, alcohol C has 1 (or 0) C atoms directly attached
-secondary, alcohol C has 2 C atoms directly attached
-tertiary, alchoho, C has 3C atoms directly attached

Question 4

how do you reduce an aldehyde?

Answer 4

aldehydes are reduced to primary alcohols by NaBH4

Question 5

do aldehydes and ketones react with nucleophiles?

Answer 5

due to polarity- aldehydes and ketones react with some nucleophiles.
nucleophile is attracted to and attacks slightly positive atom resulting in addition acorss C=C bond.
nucleophilic addition

Question 6

what does HCN do?

Answer 6

hydrogen cyanide adds across C=O bond of aldehydes and ketones. HCN is a colourless, extremely poisonous liquid that boils slightly above room temp.
produced by sodium cyanide and sulphuric acid- dangerous
reaction is useful as it increases length of carbon chain

Question 7

mechanism for nucleophilic addition to carbonyl compounds (using NaBH4)

Answer 7

-The lone pair of electrons from the hydride ion :H- is attracted to and donated to the S+ carbon atom in the aldehyde or ketone C=O bond.
-A dative covalent bond is formed between the hydride ion and the carbon atom of the C=O bond.
-The pi bond in the C=O double bond breaks by heterolytic fission, forming a negatively charged intermediate.
-the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. the intermediate has then been protonated to form an alcohol.

Question 8

how to test for ketone

Question 9

colour change when primary or secondary alcohols are oxidised

Answer 9

orange > green