Handouts for Organic Chemistry Exam

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					Handouts for Organic
  Chemistry Exam
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Systematic Nomenclature (IUPAC)
Common groups and abbreviations
                 Summary of SN1 and SN2
Type of
Haloalkane         SN 2                                    SN 1
Methyl         SN 2 is favored .              SN 1 does not occur. The methyl
CH3 X                                         cation is s o u nstab le th at it is
                                              never ob served in solution .
Primary        SN 2 is favored .              SN 1 does not occur. Primary
RCH2 X                                        carbocations are so un stable that
                                              they are never observed in s olution.
Secon dary     SN 2 is favored in aprotic     SN 1 is favored in protic solven ts
R2 CHX         solvents w ith good            w ith poor n ucleoph iles .
               nu cleophiles.
Tertiary      SN 2 does not occur because     SN 1 is favored becau se of th e ease of
R3 CX         of s teric h indrance around    formation of tertiary carbocation s.
              the s ubstitu tion center.
Su bstitution Invers ion of configu ration.   Racemization. Th e carbocation
at a          The n ucleophile attacks        intermediate is plan ar, and attack b y
stereocenter the s tereocenter from the       the n ucleophile occurs w ith equ al
              sid e op pos ite the leavin g   probability from either sid e.
              group .
                Substitution vs Elimination

• Many nucleophiles are also strong bases (OH- and RO-) and SN
  and E reactions often compete
   – the ratio of SN/E products depends on the relative rates of
     the two reactions
                               nucleop hilic
                               sub stitution H C   C Nu +   X-
                          -
     H C    C X +    Nu
                               -elimination   C C      + H-Nu + X-


    What favors Elimination reactions:
    - attacking nucleophil is a strong and large base
    - steric crowding in the substrate
    - High temperatures and low polarity of solvent
           Summary of S vs E for Haloalkanes

   – for methyl and 1°haloalkanes

Methyl       SN2       The only sub stitution reactions observed
 CH3 X       SN1       SN 1 reactions of methyl halid es are n ever observed.
                       The meth yl cation is so uns table that it is never
                       formed in solution .
Primary      SN2       The main reaction w ith strong bases such as OH - an d
  RCH2 X               EtO -. Als o, th e main reaction w ith good
                       nu cleophiles/w eak bas es, su ch as I- and CH 3 COO -.

             E2        The main reaction with stron g, bu lky bases , such as
                       potas sium t ert-butoxide.
           SN 1 / E1   Primary cation s are n ever formed in s olution; th erefore,
                       S N 1 and E1 reaction s of p rimary h alid es are never obs erved.
           Summary of S vs E for Haloalkanes

   – for 2° and 3° haloalkanes


Secondary SN 2        The main reaction w ith w eak b ases/good nu cleophiles,
  R2 CHX              such as I- and CH 3COO -.
             E2       Th e main reaction w ith s trong bases /good nucleoph iles
                      su ch as OH - an d CH 3CH 2O - .
           SN1 / E1   Common in reactions w ith w eak nucleop hiles in p olar
                      protic s olvents, s uch as w ater, methan ol, an d ethanol.

Tertiary    SN 2      SN 2 reactions of tertiary halides are n ever observed
 R3 CX                because of th e extreme crow ding aroun d the 3° carbon.
             E2       Main reaction w ith strong bas es, su ch as HO - an d RO -.
           SN1 / E1   Main reactions w ith poor nu cleophiles/w eak b ases.