What exactly is the difference between writing a general reaction and
a general mechanism for Sn1 and Sn2 reactions? I know the mechanism
includes non-bonded electrons and arrows but beyond that I am stuck.
To top it off, I am used to seeing the generic forms in the book and
seem to unable to generalize to the specific parameters below. (at
least according to my TA!)

I need to write both for the following and am very confused about how to do it...

Sn1:  1-chlorobutane plus AgNO3 as the reagent and ethanol as the nucleophile

Sn2: 2-chlorobutane as the alkyl halide and NaI as the nucleophile in acetone.

Thank you very much!

Lee

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Request for Question Clarification by andrewxmp-ga on 15 Mar 2004 20:32 PST

Hi,

I was about to set out explaining this....but realized that it will be
very difficult to show or help you with mechanisms because you need to
make detailed drawings to do so.  With only text, this is nearly
impossible.

I will offer that, general reactions are simply describing WHAT
happens in a reaction.  some examples of reactions can be found at:
[ http://courses.chem.psu.edu/chem38/reactions/reactions.html ]

Mechanisms, on the other hand, explain HOW these reactios take place. 
They are more detailed in their nature, and thus a mechanism will also
provide you with the informatio given in the general reaction.


As for SN1 vs SN2, these are two different types of mechanisms for the
process of nucleophilic substitution of an atom or functional group. 
The description of these types given by njbagel in the comments
section is quite good.  A useful page regarding this distinction can
be found at [ http://www.sienahts.edu/~swathen/organic/sn.html ]  Many
reactions, when experimental conditions are varied, can occur via
either SN1 or SN2, but the general reaction would remain the same. 
This is because, as mentioned before, the mechanism states how a
particular change comes about, but there may be more than one way for
this change to occur, and the reaction equatio only describes the
overall change.

Anyway...I hope this has helped somewhat.  Good luck with your orgo....

-Andrewxmp

Just a thought:

It has been many years since I have taken organic chemistry, however,
I do recall that SN2 reactions are unique in that they are
STEOSPECIFIC and take place with INVERSION OF CONFIGURATION.  This
means that the nucleophile (ethanol in your example) will attack the
carbon from the side opposite the bond of the leaving group (this
stereospecificity is sometimes know as a Walden Inversion).  We often
referred to an SN2 reaction as a "back attack" to remember that the
nucleophile attacks from behind the leaving group. The SN2 reaction is
actually a 1-step process depicted with an intermediate.  I would
assume that:
a)  The general reaction would depict the basic reaction in which
2-chlorobutane plus NaI yields NaCl plus 2-Iodobutane.

and 

b) The general mechanism would show the same reaction with the
intermediate.  This reaction, however, should be drawn with wedge and
dash structures; and it should defenitely show the nucleophile
attacking from behind the leaving group.  The final product is a
single stereospecific molecule.

 
The SN1 reaction, on the other hand, is a two-step process and is NOT
stereospecific - producing varying combinations of racemization.  For
this question, I assume that:

a) The general reaction simply depicts 1-chlorobutane plus ethanol
yielding a butyl alcohol plus hydrocholric acid.

and

b)  The general mechanism will show each step of the reaction using
the wedge and dash structures.  Show the dissociation, the
nucleophilic substitutions, the stereospecific products, and indicate
the fast and slow components.

I hope that at least gets you started in the right direction. 
Hopefully someone else on here will have some more to add.

-d

Thank you very much Andrew! It was quite helpful!

J- thank you very much for your help!