organic chemistry

[ruby92]

may june 2009 paper 1 no 28
no 22 hw is it free radical substitution (d) shouldn't it be B??
and no 29

[ruby92]

May june 2009 p2
Q4 part (a) the C and D box

[nid404]

June 09 paper 1
Q22) It's free radical substitution...
cause Cl radicals react with ethanoic acid.
And it can't be A and B at all cause Cl-  would be a nucleophile(nucleus loving) and not an electrophile...

Q28) 2,4 DNP reacts with carbonyls (C=O)
there's one already present
on adding acidified potassium manganate(which is an oxidising agent), it will form CO2 and COOH wherever there is a carbon-carbon double bond....
I'm sorry I couldn't explain this properly...will try looking for the compound after oxidising...so ull understand better

Q29)2-Methylbuta-1,3-diene, CH2=C(CH3)–CH=CH2 contains 5 carbons, 8 hydrogens and no oxygens
H2SO4 is a dehydrating agent...it removes water from the compound
A,B,C give rise to the monomer when water is removed
 As for D, when water is removed it doesn't hydroxyl group is secondary....it's an isomer of the monomer required

[nid404]

I'll answer the others in a while...i gtg nw

[ruby92]

could you please explain 29 again....
i really dont get it

[nid404]

hmm....

Remove 2 water molecules from each of the options...and draw their structures again....
D won't match with the monomer....try doing that

[sweetie]

HEY PPL,

cud any1 xplain Q. 29 & 24??

thanx in advance

[nid404]

q24)
Ans would be C

cause there are 2 different reaction....Each reaction will have a diff activation energy... Since the second reaction is faster, activation energy will be lower

q29) D

C=O in propanone forms a carbocation...to which CN is attached...when hydrolysed, O becomes OH, and CN turns to COOH

Revise you mechanisms well People usually go wrong in such questions

[sweetie]

Thank You

[nid404]

ur welcome

[sweetie]

hey,
Q24> da ans is C
but i thought it cud also be A
plz xplain?

Q.27> da ans. is D
but i dont get why??

Thank You!!

[ruby92]

In the forward reaction the structure given there has a COOH group as well as OH
the backward reaction cannot be addition since addition only occurs if u have a c=c bond not c=o

[ruby92]

in 27 the formula has only one O so it can either be an ester(COO) or alcohol (-OH)
the second info given here tells us that it is unreactive to mild oxidising agents
only tertiary alcohol ie c atoms that have the -OH group are attached to 3 other carbon atoms.
so when u break this bond the place where OH was will be a double bond
this atom must be surrounded by 3 others

make any sense???

[sweetie]

okayyyyyyyy!

cud u xplain Q24> in more details

Thank You

[ruby92]

ok see
the second structure shown the one with the C=O group..u see a double bond anywhere on it??
addition only occurs if the compound has a single or a double C=C not a C=O double bond is there
so u can eliminate that idea out of it.
esters can only be converted back to their original acid alcohol reactants by acid(eg H2SO4) hydrolysis
The first compund has alcohol as well as two acid groups.
these two always react togather to give an aster by esterfication in the presence of conc.H2SO4.

get it??