Question

Can someone tell me why does the reaction between alcohol and PCl5 is a nucleophilic substituition? is the nucleophile Cl- or -OH group?

Answer 1

=D

Answer 2

again a question from your multiple choice?????

Answer 3

i forgot to say hi.. :)

Answer 4

nono haha its a concept i failed to grasp because it's not explained in detailed in my syllabus.. and i cant find info on the web =(

Answer 5

lol! hi!

Answer 6

:)... no problem..... let me think..
till then .... you may try some other question.. o

Answer 7

thanks!!

Answer 8

ezizio... i can tell you about alcohol reaction with PCl3

i think it shoul be analogous to the reaction between alcohol and PCl5

Answer 9

let me search in my books....
maybe i could find something..

Answer 10

yea with pcl3 will do too

Answer 11

we know that the O in alcohol has two lone pair of electrons.
these electrons react with PCl3 in the following way:_

Answer 12

the attachment has the mechanism by which, reaction takes place.

Answer 13

where did that wierd looking compund with Nitrogen come from? o.o

Answer 14

its a base. it is pyridine. it comes from solvent,
wait til college
till then, take no worries about that.

the thing that concerns us is the presence of a base that could take up the proton.

Answer 15

hmm so the br- is the nucleophile attacking the c-o bond, correct?

Answer 16

but at the first step, it looks like oH was aacting as the nucleophile as it undergoes reaction with pbr3

Answer 17

you can see this image if the previous one bothers you....

this one does not show any weird looking molecule..

Answer 18

it... looks like a messy reaction XD

Answer 19

hmmm it makes more sense to me now!

Answer 20

br- is the nucleophile... you are absolutely right.

what the first reaction does is:-

look, this one is a substitution reaction. right?
a substitution reaction has a nucleophille and a leaving group.
leaving group must be a weak base.

don't say that you never heard things like these...
i am sure, you might have read all these things. :)

but in this reaction, cl- attacks and oh- must leave. which is not possible as oh- is a strong base and hence, can't act as a leaving group.

so, the first reaction , oh reacts with pcl3 and look at the second reaction, it's HOPBr2 that leaves and not the OH-

Answer 21

ive never heard a good leaving group has to be a weak base!! XD

Answer 22

but thx! i believe the reaction with pcl5 should be very similar =)

Answer 23

yes.. i too think so...

Answer 24

and yes... a good leaving group is a weak base..

Answer 25

but why? a weak base merely means it is unable to accept a hydrogen ion

Answer 26

again .. you did that..
typed a message and then erased it...:)

Answer 27

look.. do you know the relationship between nucleophilicity and basicity??

Answer 28

hmmm the more nucleophilic a substance is, the more basic it is?

Answer 29

yes.... absolutely...
good!!

Answer 30

so, if our leaving group is not a weak base. i.e. you may say it is a strong base, then it is a good nucleophile too.. isn't it??

and in that case, our leaving group won't simply leave but it will again attack the product and reform the reactant....

are you following this thing?

Answer 31

D= i didnt think of that!

Answer 32

THX!

Answer 33

welcome!

Answer 34

i knew a strong base means strong nucleophile because of amine groups @.@

Answer 35

the more available the lone pairs are, the more nucleophilic it is

Answer 36

yes...

Answer 37

right!

Answer 38

haha thx!