Debrief - 9746 Chemistry
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Originally posted by plasticpiranha:
i think for this question right. it is electrophilic substitution. the NO2 electrophile will not substitute the OH as the bond is already very strong due to overlapping. instead, it will substitute the hydrogen atom at the 2-directing phenol.
yah i think this paper is much much simpler than p3
neways me n my friends were arguing about dilute HNO3 for the last question
it can be acidic hydrolysis and it also can be electrophilic substitution (phenol -> nitrobenzene)?
but they clearly mentioned that there is only [b]one compound that will react for each reagent? hmmm
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Originally posted by club18:screwed la..
i guess im the only 1 in spore who get qn 1 wrong..
i look at it then wrote alkenes..
so retarded.. and careless..
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hmm 4-directing also can right?Originally posted by maxtonian:i think for this question right. it is electrophilic substitution. the NO2 electrophile will not substitute the OH as the bond is already very strong due to overlapping. instead, it will substitute the hydrogen atom at the 2-directing phenol.
btw any idea how to draw A reacting with tollen's reagent? -
dont worryOriginally posted by club18:screwed la..
i guess im the only 1 in spore who get qn 1 wrong..
i look at it then wrote alkenes..
so retarded.. and careless..
someone in my school also wrong. wrote hydrocarbon lol. -
yeah. either 2-directing or 4-directing.Originally posted by striderz_o405:hmm 4-directing also can right?
btw any idea how to draw A reacting with tollen's reagent?
the tollen reagent one. i 4got the overall compound liao, i just know shld have O=C-O-NH4+. the important thing is the NH4+ -
i tink its just 2 directing...4 is occupied by the OCH3..which is inertOriginally posted by striderz_o405:hmm 4-directing also can right?
btw any idea how to draw A reacting with tollen's reagent? -
i dont think i used COriginally posted by xxxshadowxxx:i tink its just 2 directing...4 is occupied by the OCH3..which is inert
i think i wrote B or sth. cant rmb. -
the answer shld be ccca if i am nt wrong..cos i tallied wif most of my classmatesOriginally posted by striderz_o405:i dont think i used C
i think i wrote B or sth. cant rmb. -
but i think there can be variations to answers. some answers are also acceptable.Originally posted by xxxshadowxxx:the answer shld be ccca if i am nt wrong..cos i tallied wif most of my classmates
but 1st and 3rd ques definitely C, 4th confirm A -
eh..i am nt sure..cos the question wrote tt only one for each reagentOriginally posted by striderz_o405:but i think there can be variations to answers. some answers are also acceptable.
but 1st and 3rd ques definitely C, 4th confirm A -
yeah..i also put CCCA
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what is the mechanism when you change COCl2 to COClOH?
nucleophilic sub? SN1 or SN2? or wat? -
nucleophilic substitutionOriginally posted by th3m0ment:what is the mechanism when you change COCl2 to COClOH?
nucleophilic sub? SN1 or SN2? or wat?
just do the normal way like what u did in org chem. -
organic chem nucleophilic sub gort learn 2 mthds mah. you use the transition state one or get carbocation one
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bah dun need NH4+. just the COO- group will suffice.Originally posted by maxtonian:yeah. either 2-directing or 4-directing.
the tollen reagent one. i 4got the overall compound liao, i just know shld have O=C-O-NH4+. the important thing is the NH4+
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. -
thats nucleophilic substitution...Originally posted by th3m0ment:what is the mechanism when you change COCl2 to COClOH?
nucleophilic sub? SN1 or SN2? or wat?
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
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It's decomposition. Oxidation is ruled out as Carbon's oxidation state remains unchanged.Originally posted by plasticpiranha: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 -
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. -
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 =.=Originally posted by striderz_o405:nucleophilic substitution
just do the normal way like what u did in org chem.
Not good to have so many chem pro friends around you sometimes -.- -
BINGO! your friend is so correct.Originally posted by tangjing: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 -.-
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. -
wowOriginally posted by teraexa: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.
can i just skip the intermediate step then?
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Of course you can lump everything into one step. It's H2 Chem leh. Dun think and dun worry so much.Originally posted by plasticpiranha:wow
can i just skip the intermediate step then? -
so how am i supposed to know that?
H2 chem does not even haf a negative O? -
same with p3's 3 carbonyl questionOriginally posted by th3m0ment:so how am i supposed to know that? -
that is why the question states " SUGGEST the mechanism" ma. cos not in our syllabus.
