Debrief - 9746 Chemistry

last SG · 2007-11-05T19:38:26+00:00

I interpreted alkaline to be alkaline. That's it. So given the 2 choices, I chose the salt which is a weaker conjugate base.

maxtonian SG

yeah..i also put CCCA

th3m0ment SG

what is the mechanism when you change COCl2 to COClOH?
nucleophilic sub? SN1 or SN2? or wat?

striderz_o405 SG

nucleophilic substitution

just do the normal way like what u did in org chem.

th3m0ment SG

organic chem nucleophilic sub gort learn 2 mthds mah. you use the transition state one or get carbocation one

teraexa SG

bah dun need NH4+. just the COO- group will suffice.

for the mechanism, i wrote nucleophilic substitution. however, it seems to be nucleophilic acyl substitution rather than simple SN1 or SN2 substitution. i drew the mechanism as nucleophilic acyl substitution anyway.

bah finished the paper in 45 mins, checked a bit, left 25 mins, slept for 10 mins, woke up and checked again.

55/60 is not impossible.

plasticpiranha SG

thats nucleophilic substitution...
the one im not sure is the one after that: COCl(OH) to CO2 + HCl
i know the whole thing (2 steps combined) is hydrolysis
but once they split it up i have no idea Rolling Eyes

teraexa SG

It's decomposition. Oxidation is ruled out as Carbon's oxidation state remains unchanged.

teraexa SG

For the dilute HNO3, there are 2 possibilities, either the phenol electro-sub or the hydrolysis of ester.

Between the 2, I chose the phenol one cos it's in syllabus and there are less uncertainties with regards to dil. HNO3 reacting with phenol. Was pretty uncertain whether HNO3 is strong enough an acid to hydrolyse ester.

tangjing SG

Any H3 chem people here...my friend taking H3 chem say cannot draw the mechanism for nucleophilic substitution, cause sp2 hybridised carbon cannot undergo nucleo subst....then he also say a lot of things that I was so sure is correct but ended up wrong =.=

Not good to have so many chem pro friends around you sometimes -.-

teraexa SG

BINGO! your friend is so correct.

Used to take MOE H3 Chem until I defected to NUS H3 Chem.

Your sp2 hybridised carbon cannot undergo normal nucleo-sub. The mechanism is slightly different known as nucleo-acyl substitution. Basically, when your nucleophile whack your delta-plus carbon, one of the double bond to O jumps to the O atom, hence the intermediate is a tetrahedral with a positive charge on your O atom (think nucleophilic addition intermediate). Then, the next step is one of the groups (Cl in this case) leaving and the negative charge moves back and get shared between the C and O, restoring the C=O bond.

http://www.cem.msu.edu/~reusch/VirtTxtJml/crbacid2.htm#react1b

Still rather weird for Cambridge to test on something out of H2 syllabus.

plasticpiranha SG

wow Shocked
can i just skip the intermediate step then? Razz

teraexa SG

Of course you can lump everything into one step. It's H2 Chem leh. Dun think and dun worry so much.

th3m0ment SG

so how am i supposed to know that? Evil or Very Mad H2 chem does not even haf a negative O?

plasticpiranha SG

same with p3's 3 carbonyl question Rolling Eyes

maxtonian SG

that is why the question states " SUGGEST the mechanism" ma. cos not in our syllabus. Very Happy

teraexa SG

it was in my h2 chem notes on carboxylic derivatives although explicitly labelled out of h2 syllabus. needed to know it cos er an olympiad question was also on this mechanism (ester formation).

striderz_o405 SG

expected it to appear in your chem notes. same for other top schools too.

my sch's chem notes just give the minimal.
EVEN the tollen's reagent they only give "silver mirror seen"

I HATE MY SCHOOL! Evil or Very Mad

xxxshadowxxx SG

dun worry..my notes did the same too..just talk abt silver mirror for tollens' nth else..n it is a top school fyi..

teraexa SG

or maybe it's just rj chem dept that's super kiasu. everything also dump into the notes.

i dun blame them though. best group of chem teachers i have seen. ever.

xxxshadowxxx SG

yup..i haf heard of rj's pro-ness in chem..i tink for my sch the physics dept is good..u have some good n some bad..haha..tts life..just lyk today's econs paper..haha

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