Determining Electrophilic/Nucleophilic substitution

Cyrus The Great

Hey guys,

I always get stuck on determining whether something is electrophillic substitution/elimination/addition or nucleophillic substitution/elimination/addition.

Can someone please help me out a bit. Cheers

Nucleophilic is where something is attracted to a positive charge, for example attracted to a carbocation, or a carbon attracted to a bromine.

Electrophilic is where something is attracted to a negative charge, for example hydroxide ions.

Substitution is where the thing is swapped, for example a haloalkane could be swapped for a OH group.

Elimination is where the products include a small molecule, e.g. water or a haloalkane. The small product was removed from the main reactant e.g. a haloalkane or an alcohol.

Addition is pretty straightforward, the electrophile or nucleophile is attracted to something and is added on to it.

Hope that helps!

Reply 2

It's ALWAYS Electropholic Addition and Nucleophilic Substituition

Reply 3

~*~rAiNbOw~*~

It's ALWAYS Electropholic Addition and Nucleophilic Substituition

Not always, for example the reaction between a nucleophilic bromide ion and a carbocation = nucleophilic addition.

Reply 4

Fair enough..all the equations in my exam board are either EA or NS

Reply 5

~*~rAiNbOw~*~

Fair enough..all the equations in my exam board are either EA or NS

Ah right, well then it's easy enough to remember :biggrin:

Reply 6

Lulu*et*Moi

It could be Elimination in some circumstances..or even hydration

Can't you determine the actual mechanism by whether the initial reactant has a double bond? :s-smilie:

I was talking about it being Nucleiophilic SUBSTITUTION and Electrophilic ADDITION (the ending of both words being the same); didn't say nought bout elimination and hydration...
but I don't think u can determine the type of a reaction purely on the basis of one of reactants having a double bond; you've got to know whats reacting and whats being formed.

Reply 7

Lulu*et*Moi

It could be Elimination in some circumstances..or even hydration

Can't you determine the actual mechanism by whether the initial reactant has a double bond? :s-smilie:

Well I think the only thing a double bond can be is addition, because it's unsaturated. You can't substitute a hydrogen for anything else, and you surely can't eliminate.

But simply because haloalkanes don't have a double bond doesn't tell you what mechanism there is going to be (because there are many).

Reply 8

EierVonSatan

21

jonnyofengland

Well I think the only thing a double bond can be is addition, because it's unsaturated. You can't substitute a hydrogen for anything else, and you surely can't eliminate.

Although not for A-level you can do all those things :biggrin:

Reply 9

Mos Def

17

Also if you look at the reagents you can tell, nucleophilies are normally -vely charged and have a lp of e's, and then if its adding on or substituting for something else will give you the mechanism.

Reply 10

EierVonSatan

Although not for A-level you can do all those things :biggrin:

Dammit! I knew we were lied to. We're always lied to. First they tell us the world is flat, then it's round, I wonder what shape it will be tomorrow?

Reply 11

thelostchild

10

~*~rAiNbOw~*~

It's ALWAYS Electropholic Addition and Nucleophilic Substituition

I take it you havnt done benzine chemistry yet that reacts by electrophilic substitution, you also have nucleophic addition/elimination which you can see with the reaction of an acyl chloride with an alcohol to form an ester :smile:

Reply 12

jonnyofengland

Dammit! I knew we were lied to. We're always lied to. First they tell us the world is flat, then it's round, I wonder what shape it will be tomorrow?

egg shaped.

Reply 13

PoisonDonna

14

~*~rAiNbOw~*~

egg shaped.

Yes they lie at A Level. They lie in first year degree too (and possibly after for all I know) but they don't call it lying, they call it "handwaving" :s-smilie:

Reply 14