kiiten
Badges: 18
Rep:
?
#1
Report Thread starter 3 years ago
#1
1. Describing a test tube reaction to show something is 1-chloropropane.

The mark scheme says NaOH then acidified AgNO3 produces a white ppt.

Does this mean NaOH reacts in a nucleophilic substitution reaction producing NaCl and an alcohol. Then the NaCl reacts with acidified AgNO3 produces a white ppt. ? Also does the 'acidified' mean adding dilute nitric acid?

2. A compound (C6H12O2) has a peak on the H NMR spec at d 1.2, integration value 6. What does this tell you about the structure? Use the data table linked below. I thought it would be x3 CH2 but thats wrong.

http://filestore.aqa.org.uk/subjects...W-TRB-PTDS.PDF

3. What does d 3.8 and d 2.6 tell you about the structure.For compound C6H12O2

4. Which of the following doesnt have a singlet peak in H NMR and why?


A butyl methanoate

B propyl ethanoate

C ethyl propanoate

C methyl butanoate
0
reply
kiiten
Badges: 18
Rep:
?
#2
Report Thread starter 3 years ago
#2
PLEASE someone...
0
reply
tony_dolby
Badges: 7
Rep:
?
#3
Report 3 years ago
#3
Acidified does mean adding dilute nitric acid. The first step when ou add NAOH is a nucleophilic attack by the hydroxide ion on the carbon and the chlorine leaves as a chloride ion. It is this ion that reacts with silver ions to make the white ppt. of silver chloride. If we didn't add the NaOH first, the chlorine would still be bonded to the carbon. Don't forget that silver nitrate tests for chloride ions and not chlorine atoms.
0
reply
kiiten
Badges: 18
Rep:
?
#4
Report Thread starter 3 years ago
#4
(Original post by tony_dolby)
Acidified does mean adding dilute nitric acid. The first step when ou add NAOH is a nucleophilic attack by the hydroxide ion on the carbon and the chlorine leaves as a chloride ion. It is this ion that reacts with silver ions to make the white ppt. of silver chloride. If we didn't add the NaOH first, the chlorine would still be bonded to the carbon. Don't forget that silver nitrate tests for chloride ions and not chlorine atoms.
Thanks for replying

Ah, ok so i was right about that - any idea with the other questions?
0
reply
tony_dolby
Badges: 7
Rep:
?
#5
Report 3 years ago
#5
When I see '6' I always think two methyl groups in identical chemical environments.
0
reply
tony_dolby
Badges: 7
Rep:
?
#6
Report 3 years ago
#6
Have a look at the chemical shift table and see if you can find any likely groups with the same chemical shift.
0
reply
kiiten
Badges: 18
Rep:
?
#7
Report Thread starter 3 years ago
#7
(Original post by tony_dolby)
Have a look at the chemical shift table and see if you can find any likely groups with the same chemical shift.
x2 CH3? so -C(CH3)2

I got confused because 1.2 fits into R2CH2 and RCH3
0
reply
tony_dolby
Badges: 7
Rep:
?
#8
Report 3 years ago
#8
Exactly. It's not very often that you get three CH2 groups identical in a molecule. Two methyl groups attached to the same carbon is very common.
0
reply
tony_dolby
Badges: 7
Rep:
?
#9
Report 3 years ago
#9
If the signal integrates for 6 protons it would have to be three identical CH2 groups and I don't see how that would work in a molecule that small.
0
reply
kiiten
Badges: 18
Rep:
?
#10
Report Thread starter 3 years ago
#10
(Original post by tony_dolby)
If the signal integrates for 6 protons it would have to be three identical CH2 groups and I don't see how that would work in a molecule that small.
Ah ok thanks. What about question 3?

Do you mean 3 identical CH2 groups as in 3 attached to the same carbon?
0
reply
tony_dolby
Badges: 7
Rep:
?
#11
Report 3 years ago
#11
Sort of, but it's a bit difficult to explain. Cyclohexane has identical CH2 groups for example. I wouldn't bother about this too much, just remember 6 protons represents two methyl groups in identical chemical environments. Often, in molecules like this, the only way for them to be identical is to be attached to the same carbon. In alkanes like butane, for example, they can be at opposite ends of the molecule but are identically connected.

Regarding question 3, you just need to look at the chemical shift table and find two groups that have the correct chemical shifts and that are consistent with the chemical formula. The fact that they are singlets indicates that there are no hydrogen atoms on a neighbouring carbon.
0
reply
tony_dolby
Badges: 7
Rep:
?
#12
Report 3 years ago
#12
Do you have the correct answer for question 3?
0
reply
kiiten
Badges: 18
Rep:
?
#13
Report Thread starter 3 years ago
#13
(Original post by tony_dolby)
Sort of, but it's a bit difficult to explain. Cyclohexane has identical CH2 groups for example. I wouldn't bother about this too much, just remember 6 protons represents two methyl groups in identical chemical environments. Often, in molecules like this, the only way for them to be identical is to be attached to the same carbon. In alkanes like butane, for example, they can be at opposite ends of the molecule but are identically connected.

Regarding question 3, you just need to look at the chemical shift table and find two groups that have the correct chemical shifts and that are consistent with the chemical formula. The fact that they are singlets indicates that there are no hydrogen atoms on a neighbouring carbon.
Sorry they are not singlet peaks - i got it confused with another question :3

This really confused me i got:

RCOOCH2- (for d 3.8) and RCOCH2- (for d 2.6)

The correct answer is -OCH2CH2CO-
0
reply
kiiten
Badges: 18
Rep:
?
#14
Report Thread starter 3 years ago
#14
(Original post by kiiten)
Sorry they are not singlet peaks - i got it confused with another question :3

This really confused me i got:

RCOOCH2- (for d 3.8) and RCOCH2- (for d 2.6)

The correct answer is -OCH2CH2CO-
Bump
0
reply
tony_dolby
Badges: 7
Rep:
?
#15
Report 3 years ago
#15
(Original post by kiiten)
Bump
That makes more sense. I couldn't see how the singlets would work. Can you see that your method will give you two many oxygens? It isn't just a matter of finding a chemical shift in the right region, but one which accords with the molecular formula.

If you are thinking about an ester, then that would give you two oxygens. It would give a possible answer for the peak at 3.8, but it wouldn't explain the peak at 2.6.

I am still not quite clear about the question.
0
reply
tony_dolby
Badges: 7
Rep:
?
#16
Report 3 years ago
#16
Is this it?
Attached files
0
reply
kiiten
Badges: 18
Rep:
?
#17
Report Thread starter 3 years ago
#17
(Original post by tony_dolby)
Is this it?
No that was my question 2 about the x2 CH3 - which you already helped me with.

This is the question, its part iii that im stuck on:

Name:  Screenshot 2017-05-11 07.30.49.png
Views: 343
Size:  23.2 KBAttachment 645248645250
Attached files
0
reply
tony_dolby
Badges: 7
Rep:
?
#18
Report 3 years ago
#18
Excellent. The first thing I would do with these kind of questions is to check whether the integral ratio corresponds to the number of hydrogens in the molecule. It does, so we can treat each integral as an actual hydrogen.

i) This peak is caused by a methyl group. It is a singlet so it there are no hydrogen atoms on the next-door carbons. The chemical shift indicates that this methyl group is attached to a C=O. I am now thinking 'methyl ketone'.

ii) The peak at 3.5 integrates for 2 hydrogens so it is a CH2 group. It is a quartet so it is connected to a CH3 group. The chemical shift indicates that it is singly bonded to an oxygen. The peak at 1.2 integrates for 3 protons so it is a methyl group. It is a triplet so it is next to a CH2.

iii) The peak at 3.8 integrates for 2 protons so it is CH2. It is a triplet so it must be next to one CH2. The chemical shift indicates that is singly bonded to an oxygen. We now have found the thing that is the other side of the singly bonded oxygen!

The peak at 2.6 integrates for two protons so it is a CH2. The chemical shift shows that it is next to a C=O on one side. It is a triplet, so it must be next to a CH2 on the other.
0
reply
tony_dolby
Badges: 7
Rep:
?
#19
Report 3 years ago
#19
Here you go. I have simulated an NMR spectrum and it is correct.
Attached files
0
reply
tony_dolby
Badges: 7
Rep:
?
#20
Report 3 years ago
#20
Spectrum
Attached files
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Do you have the space and resources you need to succeed in home learning?

Yes I have everything I need (325)
56.13%
I don't have everything I need (254)
43.87%

Watched Threads

View All
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise