[CasualSoul]

Been going over this for hours...but it's doing my head in

First of all ketones. This is what I'm doing:identify parent chain, number from end closest to carbonyl location 3) Identify the branches 4) ends in one. I understand these steps. I know you put in numbers for methyl etc. However, I'm so confused on whether you have to put in a number to show the location of the carbonyl group.


Secondly, aldehydes.. this is frustrating me to . I get all the steps and everything and that you would put in numbers to show where methyl groups are etc. But again, I'm confused on whether you have to show the position of the carbonyl group with a number.

[Einy]

In aldehydes you dont have to label the position of the carbonyl group in the molecule because it is for the purposes of A level certainly always on carbon 1. In ketones which have a hydrocarbon chain length of five or more you do need to label the position of the carbonyl group because multiple structural isomers are poissible.

[DarkAndTwisty]

(Original post by CasualSoul)
Been going over this for hours...but it's doing my head in

First of all ketones. This is what I'm doing:identify parent chain, number from end closest to carbonyl location 3) Identify the branches 4) ends in one. I understand these steps. I know you put in numbers for methyl etc. However, I'm so confused on whether you have to put in a number to show the location of the carbonyl group.


Secondly, aldehydes.. this is frustrating me to . I get all the steps and everything and that you would put in numbers to show where methyl groups are etc. But again, I'm confused on whether you have to show the position of the carbonyl group with a number.

You would have to put the number in for the -one group, for example pentan-2-one. You also have to put the numbers in for the methyl and ethyl groups for example 3-ethylpentan-2-one (these are just examples, idk if they're actual molecules) or 3.4-dimethylpentan-2-one.

You wouldn't have to put the number before the -al in an aldehyde as at A level the functional group will be at the end of the chain. You would however have to number the other groups, as usual

I hope that made sense, I tend to not make sense after five o'clock If you have any more questions, I'll try and help you!

[CasualSoul]

Yeah, that really helped for carboxylic acids do you need to include the position so like pentan-2-oic acid ...this sounds wrong so I'm thinking you don't?

[DarkAndTwisty]

(Original post by CasualSoul)
Yeah, that really helped for carboxylic acids do you need to include the position so like pentan-2-oic acid ...this sounds wrong so I'm thinking you don't?

Nope, because the carboxylic acid group will be on the end of the chain, as the C has to double bond to the oxygen and has to bond to the OH group, so there is only 'space' for one more bond, so it has to be at the end.

[CasualSoul]

oh right. Great stuff! Thanks again