Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
12 Cards in this Set
- Front
- Back
|
describe the structure of aldehydes and ketones |
aldehydes = carbonyl group is at the end of the carbon chain and so has at least one hydrogen attached to it suffix= al ketones = the carbonyl group is in the middle of the carbon chain so has 2 alkyl groups attached to it. suffix = one |
|
|
can aldehydes and ketones be distinguished by their molecular formula. if not how are they represented. |
no because they have the same functional group so they are therefore represented their displayed or structural formulas |
|
|
how are aldehydes prepared from alchols |
- prepared by the oxidation of a primary alcohol by oxidising agents such as acidified potassium dichromate paper. - in order to isolate the aldehyde the product is distilled directlyfrom the reaction mixture.if this wasnt done the aldehyde would further oxidise to a carboxylic acid. |
|
|
how are ketones prepared from alcohols |
- prepared by the oxidation of secondary alcohols by acidified potassium dichromate paper - the secondary alchol is refuxed with the oxidising agent - it is not necessary to distil the ketone from the reaction mixture because it cannot be oxidised further. |
|
|
describe the soluability of aldehydes and ketones |
the carbonyl group is polar due to the greater electronegstivity of oxygen. soluability small aldehydes and ketones are soluable in water due tohydrogen bonding between a lone pair on the oxygen and the hyderogen of the water as size increases the soluability decreases due to interference in hydrogen bonding by the hydrocarbon tails of the aldehydes and ketones |
|
|
describe theboiling point of aldehydes and keones |
lower than an alchol but bigger than an alkane. this is due to intermolecular forces. alkanes = van der waala forces aldehydes and ketones= van der waals and dipole dipole interactions alchols= van der waals,dipole dipole and hydrogen bonding |
|
|
describe the reactivity of the carbonyl group |
- although double bonds require more energy to break than single bonds. compounds with double bonds tendtobe more reactive as addition reactions are possible - some of the chemical properitie of aldehydes and ketones result from the polar nature of the C=O bond - the postitve charge on the carbon makes it oprn to attack by nucleophiles - aldehydes and ketones can be reduced to alcohols - aldehydes may also be oxidised to carboxylic acids |
|
|
describe the reduction of aldehydes |
-reduced to primary alcohols by NaBH4 ( hydride ion) - the lone pair on the hydride ion is attracted to the partial positive charge on the carbonyl carbon. the elctrons in the C=O bond are replled to the electronegative oxygen atom - this reults in thhe formation of an intermediate with a lone pair and a negaitve charge on the oxygen atom of the aldehyde - a H+ ion acts as an electrophile and is attacked by the oxygen atom from the intermediate. - the lone pair on the oxygen is attracted towards the positively -charged H+ and forms a covalent bond - this results in the formation of a primary alcohol |
|
|
describe the reduction of ketones |
- reduced to secondary alchols by NaBH4 (hydride ion) -same mechanism as aldehydes just results in the formationn of a secondary alcohol. |
|
|
describe nucleophillic addition using cyanide |
- the positive chare on the carbon is open to attack by nucleophiles which is used to extend the length of the carbon chain - the one pair on the cyanide ion is attracted to the partial ositve charge on the carbon and the elctrons in the C=O bond are repelled to the electronegative oxygen atom - this results in te formation of an intermediate with a lone pair and a negative charge on the oxygen atom - then the H+ ion acts as an electrophile and is attacked by the oxygen atom of the intermediate. - the lone pair on the oxygen is attracted towards the positively charge H+ and forms a covalent bond - if the CN- is the nucleophile a hydroxynitrile is formed |
|
|
describe the dangers of HCN |
- high volatile liquid which has a faint bitter almond smell - in a solution HCN partially dissociates HCN(aq) ---> H+(aq) + CN-(aq) reversible reaction - highly toxic as it inhibits a mitochondrial enzyme that is essential for respiration - it is difficult to handle due to it being voliile and flammable - a safer alternative is potassium cyanide whicch is a solid at room temperature and easier to handle. |
|
|
What reducing agents are used for aldehydes and ketones |
NaBH4 or LiAlH4 |
