Chemistry: Post your doubts here!

[Amber]

oooh right okay thannxx

no prob
hope u got it =)

 

[daredevil]

no prob
hope u got it =)

yeah i did... but who's to say what the next question will hold in store :')

and hey wud u happen to be some sort of an expert in nmr? nmr and organic are kinda not my strong suits in chem and shout out PROBLEM the loudest for me... if u cud help.... )

 

[Amber]

yeah i did... but who's to say what the next question will hold in store :')

and hey wud u happen to be some sort of an expert in nmr? nmr and organic are kinda not my strong suits in chem and shout out PROBLEM the loudest for me... if u cud help.... )

ive got problems with nmr questions too but i could try helping =)

 

[chocolate_girl]

What is an acylchloride and how does it help on formation of carboxylic acid?

 

[daredevil]

What is an acylchloride and how does it help on formation of carboxylic acid?

R of course is a C chain on the molecule.

acyl chloride + H2O --> carboxylic acid + HCl

it is a spontaneous and vigorous reaction in which white fumes are observed immediately.

 

[chocolate_girl]

View attachment 39017


R of course is a C chain on the molecule.

acyl chloride + H2O --> carboxylic acid + HCl

it is a spontaneous and vigorous reaction in which white fumes are observed immediately.

Thankyou soo soo much can u also tell me the reaction between RNH2 and R'COCl and hydrolysis of amides

 

[daredevil]

Thankyou soo soo much can u also tell me the reaction between RNH2 and R'COCl and hydrolysis of amides

RNH2 + R'COCl --> R'CONH2 + HCl

There are two types of hyddrolysis of amides...
i) Acidic Hydrolysis:

RCONH2 + H2O --(H+ and heat)--> RCOOH + NH3

ii) Basic Hydrolysis:

RCONH2 + NaOH --(heat)--> RCOONa + NH3

 

[chocolate_girl]

RNH2 + R'COCl --> R'CONH2 + HCl

There are two types of hyddrolysis of amides...
i) Acidic Hydrolysis:

RCONH2 + H2O --(H+ and heat)--> RCOOH + NH3

ii) Basic Hydrolysis:

RCONH2 + NaOH --(heat)--> RCOONa + NH3

Thanks once again and another thing what is the compound R'CONH2 called and that the R in it is the carbon chain of acyl chloride only and wont v use the carbon chain of amide?

 

[daredevil]

Thanks once again and another thing what is the compound R'CONH2 called and that the R in it is the carbon chain of acyl chloride only and wont v use the carbon chain of amide?

I'm sorry i didnt quite catch ur question...

 

[daredevil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_42.pdf

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_ms_42.pdf

Q 3 c... y is another compound made?? is it like instead of C a cmpound D is made or what??

 

[Grenade]

Who has an idea of the likely practical questions in paper 3 for 2014

 

[syed1995]

actually i was going to ask u the same question too...


A star syed1995 MustafaMotani u guys have any idea how to do this?? it's Q7 of May/June 2013 Paper 42

NMR are Nasty.. anyway I'll give it a shot.

part (ai) M:M+1 is used for number of carbon atoms.. 100/1.1 * 3.35/43.3
= 7 Carbon Atoms



(aii) The ratio between M and M+2 peak is 3:1 meaning it's Chlorine.
PS: If it were 1:1 it would have been Bromine.



(aiii) NMR Spectrum shows 3 lines at different ppm so it has 3 different types of hydrogen environments.

NOTE THAT: Compound L reacts with sodium metal. MEANING THAT IT HAS -OH Group in it. Now we continue forward with the questions
(aiv)
Let's find the formula of the compound first.. The mass of the compound is 142. There is 7C present 1Cl present 1OH present.. and the rest are going to be H.

so 142= 7C+1Cl+1OH+XH
142=(7*12)+(1*35)+(1*17)+(X*1)
X=6
So Formula is C7(Cl)H6(OH)

Notice we have 7 Carbon atoms.. Our teacher has said whenever you have no. C>6 It's 90% a Benzene ring..
Now let's look at the Chemical shifts..
starting with the one on the very left. It has 4 written over it meaning it has 4 H attached in this environment. The chemical shift is 7-7.5

7-7.5 has Benzene ring with an H attached with it. It has 4H in this environment meaning our structure is now a benzene right with 4H.

Cl cuz we were given a M+2 Peak given at the start.

Now let's look at the middle peak. It has 2H over it so it's probably a -CH2- group. we'll come to it later.

now the peak at the very right is 1H peak.. 99% of the time 1H peak represents -OH as far as our course is concerned.

So final structure will be something like

Now we have to confirm whether this structure is correct or not.

The formula we derived was (Cl)C7H6OH
We know that there is a halogen present (Cl) from the M+2 Peak. We know that there are 7C atoms present from M+1 Peak. We know that there is a benzene right present with 4H.

Now compare that with what we have made.

• There are 4H present in the Benzene Ring - Check
• There is a environment present with 2H. CH2 present - Check
• There is an alcohol present which is not a phenol - Check
• There is a Halogen present - Check

 

[chocolate_girl]

I'm sorry i didnt quite catch ur question...

I ll rephrase it

What is the compound R'CONH2 called?
And as u said there is a reaction RCOCl+R'NH2 and product is R'CONH2 the R here is the R of R'NH2 so where did the R for RCOCl go?

 

[chocolate_girl]

Please give me the reaction of one of the group 2 elements with each of the following
element+dilute ac
Element oxides, hydroxides and carbonates with water and with dilute acids

 

[periyasamy]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

 

[periyasamy]

I ll rephrase it

What is the compound R'CONH2 called?
And as u said there is a reaction RCOCl+R'NH2 and product is R'CONH2 the R here is the R of R'NH2 so where did the R for RCOCl go?

The rcocl reaction with rnh2,,,,iS SUCH THAT the rcocl act as an acid(rcooh)...The product will actually belike ester,----->RCONH2R'..

 

[A star]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

well basically the no of sidechains effect the packing of the layers of the polymer, closer the layers are in Poly(ethene) the more effective the packing becomes due to vanderwalls forces. So they just wanted you to show efficent packing in HDPE with no or lesser ammount of sidechains and distorted packing in the LDPE.
now for d(ii)
well for any object to conduct electricity it ust have a sea of delocalised electrons or in the case of polymers their p-orbitals must overlap in order to transfer e-s from one end to another and must be planer. I am still unsure about being planer or not :/

 

[Namehere]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

Q8(a) - For the diagram you are supposed to show that LDPE has a lot of side chains and because of this the straight chains can´t pack together as closely - you can see it as if there were "waisted space", so because of the branching there is more "empty" space between the chains and hence LDPE is lower in density. HDPE is just the reverse arguments, with many fewer side chains and the staight chains can pack much more closely together so that all the polymer is contained in a smaller space, hence the higher density.

Q8(dii) - I´m not sure if I´m right so if im wrong please do someone correct me. The molecule will need to be planar. Main reason is that if you have another molecule at the top or at the bottom, for the electrons to "jump" up or down (i.e. conduct) the pi bonds of the above/bottom molecule would need to overlap with the "middle" molecule, and for them to overlap, they have to lie in the same plane, hence why it would need to be planar.

Hope it helps.

 

[periyasamy]

well basically the no of sidechains effect the packing of the layers of the polymer, closer the layers are in Poly(ethene) the more effective the packing becomes due to vanderwalls forces. So they just wanted you to show efficent packing in HDPE with no or lesser ammount of sidechains and distorted packing in the LDPE.
now for d(ii)
well for any object to conduct electricity it ust have a sea of delocalised electrons or in the case of polymers their p-orbitals must overlap in order to transfer e-s from one end to another and must be planer. I am still unsure about being planer or not :/

thanks buddy!!!

 

[periyasamy]

Q8(a) - For the diagram you are supposed to show that LDPE has a lot of side chains and because of this the straight chains can´t pack together as closely - you can see it as if there were "waisted space", so because of the branching there is more "empty" space between the chains and hence LDPE is lower in density. HDPE is just the reverse arguments, with many fewer side chains and the staight chains can pack much more closely together so that all the polymer is contained in a smaller space, hence the higher density.

Q8(dii) - I´m not sure if I´m right so if im wrong please do someone correct me. The molecule will need to be planar. Main reason is that if you have another molecule at the top or at the bottom, for the electrons to "jump" up or down (i.e. conduct) the pi bonds of the above/bottom molecule would need to overlap with the "middle" molecule, and for them to overlap, they have to lie in the same plane, hence why it would need to be planar.

Hope it helps.

Thanks buddy!!!