[boromir9111]

Hey there, the exam question question i was looking at wasn't an ester but had only a carbonyl bond and not an ester and i didn't look at the compound carefully which is a silly mistake on my side but you are right, the answer is 4 because like you said the oxygen's are in different environments. I get that but back to my exam question where the compound is
CH3CH2C=0CH2CH3...... my answer was initially 1 peak because even though the carbonyl is there the -CH3CH2 are in the same environment either and for that reason i said 1 and would have a relative peak area of 5. But of course that wasn't right, can anyone explain that to me in detail please why that is?

[charco]

Originally Posted by boromir9111

Hey there, the exam question question i was looking at wasn't an ester but had only a carbonyl bond and not an ester and i didn't look at the compound carefully which is a silly mistake on my side but you are right, the answer is 4 because like you said the oxygen's are in different environments. I get that but back to my exam question where the compound is
CH3CH2C=0CH2CH3...... my answer was initially 1 peak because even though the carbonyl is there the -CH3CH2 are in the same environment either and for that reason i said 1 and would have a relative peak area of 5. But of course that wasn't right, can anyone explain that to me in detail please why that is?

Each of the two carbons in CH3CH2 is in a different environment and so the hydrogens will have different shifts.

The first carbon is attached to three hydrogens and one carbon, the second carbon is attached to one carbon, one oxygen and two hydrogens. Magnetically these are very differnt environments.

As they are in different environments the hydrogens will also form splitting patterns.

[EierVonSatan]

Originally Posted by boromir9111

Hey there, the exam question question i was looking at wasn't an ester but had only a carbonyl bond and not an ester and i didn't look at the compound carefully which is a silly mistake on my side but you are right, the answer is 4 because like you said the oxygen's are in different environments. I get that but back to my exam question where the compound is
CH3CH2C=0CH2CH3...... my answer was initially 1 peak because even though the carbonyl is there the -CH3CH2 are in the same environment either and for that reason i said 1 and would have a relative peak area of 5. But of course that wasn't right, can anyone explain that to me in detail please why that is?

Ooops

So you have a ketone: CH₃CH₂COCH₂CH₃

If you were to draw a line of reflection down the C=O bond you will notice the compound is symmetric. This means the CH₃CH₂ parts are equivalent BUT the red and blue parts are different - each is a different distance from the C=O group and so are not in equal environments

So you would expect two peaks, one for the red protons and another for the blue protons with ratio 3:2

make sense?

edit: what charco said

[boromir9111]

I get what you mean and i figured it was that but i read on chemguide that it would be just one peak but i probably misinterpreted it and now i know. Thank you very much guys

[=gabriel=]

Originally Posted by tullybow

It was actually a First class Masters degree in Chem mate... the point is although 4 is the correct answer in practice different exam boards teach different things (sometimes these are not always correct). so to clarify...the answer is 4 but the the examiners may be marking from a scheme which sees the ester functionality as a unit rather than oxygen atoms in two different environments.

What I meant is that I did chemistry at the same level too (Edexcel A-level) and know what assumptions we were asked to make so my answer to the question was based on my experience of A2 chemistry and not just degree-level chemistry. Nothing to do with questioning your background, I'm a masters student too and to be honest there are some postdocs on this forum so we're hardly the highest authority.

[tullybow]

Originally Posted by =gabriel=

What I meant is that I did chemistry at the same level too (Edexcel A-level) and know what assumptions we were asked to make so my answer to the question was based on my experience of A2 chemistry and not just degree-level chemistry. Nothing to do with questioning your background, I'm a masters student too and to be honest there are some postdocs on this forum so we're hardly the highest authority.

Nah your fine...didn't some on here to get into an argument - just to give some guidance like yourself. Appreciate your message there.