Organic Chemistry I: Crash Course Part 3

(1) Structure of organic molecules
(a) connectivity and structural isomerism
(b) electron delocalization and drawing/evaluating resonance contributors
(c) conformational analysis (draw/evaluate chair forms and Newman projections)
(d) stereochemical analysis (E/Z alkenes; 1, 2 similar, or 2 dissimilar stereocenters)
(2) Prediction and explanation of Bronsted Acid-Base reactions (use of pKa table)
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(3) Reactions of polar C-X sigma bonds (SN and E reactions & mechanisms)
(4) Electrophilic addition reactions of C-C pi bonds (regioselectivity & mechanisms)(a) addition of H/eN (strong & weak Bronsted acids)
(b) addition of X/eN (halogenation; halogens & other nucleophiles)
(c) oxidation (mCPBA; OsO4; ozonolysis)
(d) reduction (hydrogenation with regular & poison catalyst; dissolving metal redn)
(5) EAS: Electrophilic Aromatic Substitution (regioselectivity & mechanisms)

Welcome back to part 3 of our Organic Chemistry series. This portion will be about SN and E mechanisms. SN mechanisms are more commonly referred to as substitution mechanisms whereas E mechanisms are more commonly referred to as elimination
mechanisms.

Common Examples of the following:
Protic Solvents: H2O, EtOH, CH3OH , MeOH
Aprotic Solvents: Acetone, I-, CN- , DMSO, DMF
Bulky or Sterically Big Base: tert-butanol
Small Base: OH- , OCH3- , EtO-

Summary Table from “The Organic Chemistry Tutor”

So that’s clearly a lot of information, however, there is still more to know about each of these mechanisms! Make sure to know what it means for the substrate to be primary substituted, secondary and tertiary. Also note the first substrate is known as a methyl.
In the case, for example, where SN1/E1 are in the same box that is because they both will form and often as a racemic mixture.

SN2 reaction
This is the first reaction classes start with here’s whats important to know:
-Inversion will occur for primary carbons and stereochemical inversion will occur for secondary carbons. SN2 is very very unlikely for tertiary substituted carbons. Furthermore, methyls will always preform SN2.
-there is no carbocation intermediate
-substitutions are favored over eliminations in cold or unheated conditions
-it is referred to as an “Umbrella” because of the inversion
-make sure to understand a Transition State. These have partial negative and positive charges to show where bonds will be breaking and forming.

SN1 reaction
Here’s whats important to know:
-SN1 unlike SN2 does not result in inversion and doesn’t occur in methyls.
-there is a carbocation intermediate after the LG (leaving group leaves)
-substitutions are favored over eliminations in cold or unheated conditions
-the carbocation intermediate can undergo REARRANGEMENT for stability purposes as needed.
-SN1 often forms along with E1 products. The ratio of which mechanisms product predominates depends on a lot of factors, but in most cases is a racemic mixture.

E2 Reaction
Here’s whats important to know:
-there is the loss of a LG (similar to SN2) and there is no carbocation intermediate
-there is the formation of a pi bond or multiple bond
-the base attacks the Hydrogen which forms a pi bond and results in the LG leaving.
-the Hydrogen and the LG are often “ANTI” to each other

E1 Reaction
Here’s whats important to know:
-there is a carbocation intermediate and the possibility of rearrangement occurring to increase the stability
-E1 will often form product of a reaction along with SN1 as a racemic mix.
-The LG will leave first and that will result in a C+. Then the Base will come in and deprotonate resulting in a multiple bond (pi bond) forming.