TA Robert teaches an organic lab with 8 students. This week they are studying su
ID: 860349 • Letter: T
Question
TA Robert teaches an organic lab with 8 students. This week they are studying substitution and elimination reactions.
The prep person has set out 8 bottles containing:
bromomethane sodium methoxide
bromoethane sodium t-butoxide
2-bromopropane methanol
2-bromo-2-methylpropane sodium cyanide dissolved in acetone
Events conspire against TA Robert. He arrives late at lab and the students and each student has already taken one bottle each. Even worse, the bottles were arranged in a particular order but were not labeled. He also lost his master seating chart and can
Explanation / Answer
let the names of the students be
A , B , C , D , E , F , G , H respectively
boys are B, D, F , H
Point 2) says boys sit in first 4 places
B,D,F,H----- First 4 places
A,C,E,G-----last 4 places
point 3) says B,C,E,H took black caps.
ie., they took the reagents.
out of them B,H are boys.
point 4) says students in even seats tookk bottles with green caps.
ie., they took the haloalkanes.
so in the first four places 4 boys are there.
out of them 2 boys B,H took black caps.
so they should be placed in odd places inorder
to place D,F in even places and they should take green cap.
same goes for the girls.
girls C,E took black caps.
so they should be places in odd places
therefore A,G should be placed in even places and they should take
green caps.
point 5) says F is at position 4.
since D,F are in even positions in the first 4 places.
this implies D should be at 2.
point 12) says that H sits on a end.
we know B,D,F,H sits in first 4 positions
if he has to be placed on an end.
he should be placed in the first position.
so now first 4 positions will be as
H , D , B , F respectively.
point 10) says F , E are dating so they sit next to each other.
now F is at 4 place so E should be at 5 place.
since among girls E,C should be at odd places.
E has taken 5 place so C should take 7 place.
point 6) it says that position number 6 doesnot react with H.
ponit 7) says that H reacts with A,D and F
H doesnot react with only one that is G.
and it should be placed at place 6.
therefore the positions are in the order
H , D , B , F , E , G , C , A respectively.
point 6) person in seat 6. ie., G cannot react with H.
so G is teritiary ie.,
G is 2-bromo-2-methylpropane.
point 7) H reacts with everything except G.
so H is sodium cyanide dissolved in acetone.
acetone is a polar aprotic solvent which makes
sodium cyanide a very good nucleophile undergoing SN2.
point 8) E can only react with G
where we know that G is 2-bromo-2-methylpropane.
and it is teritiary
so E must be methanol.
and it can give a mixture of ppt and colour change
because of SN1 and E1 mechanisms respectively.
point 9) person in seat 2 ie., D
ppt with B and colour change with C.
so D must be a secondary alkyl halide inorder to do so.
therefore D is 2-bromopropane.
and B is sodium methoxide and C is sodium t-butoxide
point 13)
we have left with 2 options ie., bromomethane and bromoethane
here we already decided that C is sodium t-butoxide
it itself has a lot of steric hindrance.
and we have to get ppt with both sodium methoxide
and sodium t-butoxide.
inorder to lessen any further steric hindrance our 8 place
compound ie., A should be bromomethane
this leaves us at F -- bromoethane
1 - H - Henry - sodium cyanide dissolved in acetone
2 - D - Doug - 2-bromopropane
3 - B - Bobby - sodium methoxide
4 - F - Frank - bromoethane
5 - E - Erin - methanol
6 - G - Grace - 2-bromo-2-methylpropane
7 - C - Candy - sodium t-butoxide
8 - A - Alice - bromomethane
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