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Ochem 2012 Review Guides .pdf



Original filename: Ochem-2012-Review-Guides.pdf
Title: TPR O-chem Chapter 1
Author: Mcallister

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O-Chem Day 1-Basics
Nomenclature
Nomenclature
1) Find the longest continuous carbon chain to determine base name.
2) Number the carbons, starting on the end closest to the first sutstituent.
3) Name the substituents attached to the chain. Use the chain number as the locator. Multiple
substituents use di-, tri-, tetra- etc.
4) List substituents in alphabetical order. Ignore numerical prefixes and hyphenated prefixes
(tert- and sec-), but no iso- and cyclo-.
5) If there is more than one way of numbering the chain to give the substituents the lowest
possible numbers, rank the substituents by alphabetical order giving the lower number to
the substituent beginning with the the letter closer to ‘A.’
6) If there is more than way of to come up with the longest parent chain, then choose the one
with the most substituents.

Bonding and Geometry
Electron
Hybridization
Domains
2
sp
3
sp2
4
sp3
Sigma and Pi Bonds

Bond Angle

Geometry

180
120
109.5

Linear
Trigonal planar
Tetrahedral

1 meth
2 eth
3 prop
4 but
5 pent
6 hex
7 hept
8 oct
9 non
10 dec
11 undec
12 dodec

Physical Properties of Hydrocarbons
Intermolecular Forces
1) Hydrogen Bonding – a super strong dipole-dipole force
-must have hydrogen bonded to F, O, or N to H-bond as a pure liquid
- only need F, O, N to hydrogen bond with protic compounds
2) Dipole-Dipole Forces – interaction between molecules having permanent dipole moments
-the larger the dipole moment, the larger the force
3) London Dispersion Forces – weak interactions due to a transient (temporary) dipole
-all molecules have these; the larger the molecule, the larger the force
Effects on melting pt and boiling pt
Branching (usually) decreases the boiling pt, but increases the melting pt

Solubility – Like dissolves like.

Ranking Boiling Points
1) Network Covalent (Cdiamond , SiO2)
2) Ionic
3) Hydrogen Bonding
4) Dipole-Dipole
5) London Forces

1

Miscellaneous
Nucleophiles and Electrophiles
Most strong nucleophiles have a negative charge (must have lone pairs of electrons)

Nucleophile Strength
in Aprotic Solvents

Nucleophile Strength
in Protic Solvents

C N OF
Cl
Br
I

C N OF
Cl
Br
I

Common Electrophiles

R2

O
R

X

R

R'

R1

R3

Reaction intermediates (carbocations, radicals, carbanions)
Carbocation Stability
Radical Stability
Carbanion Stability
3 > 2 > 1 > Me
3 > 2 > 1 > Me
Me > 1 > 2 > 3
Resonance Stabilization (electron delocalization)
Inductive Effects
Oxidation/Reduction Rxns (Identifying)
Degrees of Unsaturation (CNH2N+2)

Ranking Acids and Bases
1) Charge - More negatively charged species are typically more basic, and more positively charged species
are typically more acidic.
2) Atom - The larger and/or more electronegative the atom with a negative charge, the more stable it is.
3) Resonance stabilization.
4) Dipole Induction - Electron withdrawing groups (i.e., electronegative atoms) near the atom that has the
negative charge stabilize the ion/molecule.
5) Orbitals – a pair of electrons is more stable as follows: sp > sp2 > sp3

2

O-Chem Day 2 – Isomers, Newman Projections, Cycloalkanes, Substitution, Elimination
Isomerism

Chiral compounds have non-superimposable (non-identical) mirror images called enantiomers.
Achiral compounds have mirror images that are superimposable (identical).
Chiral compounds are said to be optically active.
A 50/50 mixture of enantiomers is called a racemic mixture and is optically inactive.
Chirality centers are tetrahedral centers with four different substituents (i.e. asymmetric centers).
R vs. S
Fischer projections
Multiple chiral centers
Diastereomers
Meso compounds (achiral but having chiral centers)
Amine inversion
Chiral molecules with no chiral centers

Newman Projections
Staggered, eclipsed, anti, gauche
Cycloalkanes
Ring strain
Chair Conformations of Cyclohexane
Equatorial positions are lower in energy (i.e. more stable) than axial positions due to 1,3-diaxial interactions

3

Substitution Reactions
SN2 reactions – Substitution Nucleophilic Bimolecular
Mechanism
R2

R3
R2

Nuc

Nuc
R1

+

X

R3

X
R1

rate = k[substrate][nucleophile]

SN1 reactions – Substitution Nucleophilic Unimolecular
Mechanism
+

X

Nuc

X

+

X

Nuc

Rate = k[substrate]

SN2 vs. SN1
Electrophile
Nucleophile
Solvent
Leaving Group
Rearrangements
Inversion

SN2
CH3 > 1 > 2
strong required
polar aprotic (preferred)
Good (I->Br->Cl->F-)
Not Possible
Yes

SN1
3 > 2
weak is ok
polar protic
Good (I->Br->Cl->F-)
Possible
No (Racemization)

polar aprotic solvents include DMSO, acetone, DMF, and acetonitrile, ethers
aryl and vinyl halides are unreactive (leaving group can’t be on an sp2 carbon)
nucleophile strength in aprotic and protic solvents

4

Elimination Reactions
E2 reactions – Elimination Bimolecular
Mechanism
H3C CH3

B

H
X
H H

rate = k[substrate][base]
H and X (leaving group) should be anti-coplanar (anti-coplanar)
Forms most substituted double bond (Zaitsev’s Rule)
Forms least substituted if substrate is 3 and if a bulky base is used like t-butoxide (CH3)3COE1 reactions – Elimination Unimolecular
Mechanism
H3C CH3
H

H

B

X
H H

H H

Rate = k[substrate
Forms most substituted double bond (Zaitsev’s Rule)
E2 vs. E1
Electrophile
Base
Solvent
Leaving Group
Rearrangements
Stereochemistry

Electrophile
Nucleophile/Base
Solvent
Leaving Group

E2
3 > 2>1
strong base
polar aprotic (preferred)
Good (I->Br->Cl->F-)
Not possible
Anti-coplanar

SN2
CH3 > 1 > 2
strong nuc
polar aprotic
good

E1
3 > 2
weak base
polar protic
Good (I->Br->Cl->F-)
Possible
None

E2
3 > 2>1
strong base
polar aprotic
good

SN1
3 > 2
weak nuc
polar protic
good

E1
3 > 2
weak base
polar protic
good

5

Substitution/Elimination Map

6

O-Chem Day 3: Alkene/Alkyne Rxns, Halogenation and EAS
Electrophilic Addition Reactions
Reagents
What’s
Regioselectivity Stereose Intermediate
added
lectivity
HBr (or HCl, HI)
H+ and BrMarkovnikov
carbocation
+
+
H3O
H and OH
Markovnikov
carbocation
H+, ROH
H+ and ORMarkovnikov
carbocation
Br2/CCl4 (or Cl2)
Br+ and BrAnti
bromonium ion
+
Br2/H2O
Markovnikov
Anti
bromonium ion
Br and OH
Cl2/H2O
Cl+ and OHBr+ and ORMarkovnikov
Anti
bromonium ion
Br2/ROH
Cl2/ROH
Cl+ and OR(1) Hg(OAc)2, H2O
H+ and OHMarkovnikov
Anti
mercurinium
(2) NaBH4
ion
+
(1) Hg(OAc)2, ROH
H and OR
Markovnikov
Anti
mercurinium
(2) NaBH4
ion
.
+
(1) BH3 THF
AntiSyn
H and OH
(2) H2O2, OH-, H2O
Markovnikov
H2/catalyst
H and H
Syn
(Catalyst = Pt/C, Pd/C, or Ni)
HBr/ROOR (peroxide)
H. and Br.
Antiradical
Markovnikov
(1) RCO3H
OH and OH
Anti
(2) H3O+
(1) OsO4
OH and OH
Syn
(2) H2O2
KMnO4 (cold, dilute)/ OH- OH and OH
Syn
Alkynes
Reduction (Addition of Hydrogen)
H2
H2
Pd/C
Pd/C
H2
Lindlar's
catalyst

Rearrange
ments
Possible
Possible
Possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible
Not possible

Na
NH3(l)

Addition of H2O
H2SO4

OH

tautomerization

+

O

+

OH

O

Terminal alkynes require HgSO4 as a catalyst (Markovnikov)
O
HgSO4
tautomerization
H2SO4
OH
Hydroboration oxidation with a terminal alkyne produces an aldehyde (anti-Markovnikov)
HO
H
1. (Sia) BH THF
tautomerization
2

2. H2O2, OH-, H2O

O

7

Nucleophilic Addition of Acetylide Ions
(A strong nucleophile)
An acetylide ion attacks 3 typical electrophiles:
1) an alkyl halide
2) a carbonyl (C=O)

3) an epoxide (adds to least substituted side)

Organometallic Reactions
Formed by combining an alkyl halide with Li or Mg

R X

+

2Li

R

Li

+

LiX

R X

Mg
ether

R MgX

1) an allylic or benzylic halide

+

Br

MgBr

MgBr2

2) a carbonyl (C=O)

MgBr

+

O

H3O+

MgBr+ O

3) an epoxide (adds to the least substituted side)
O
MgBr

+

O MgBr+

HO

H3O+

+

Mg(OH)Br

OH

Oxidative Cleavage of Alkenes
Reducing conditions
B. (1) O3, -78C (2) Zn/H2O or (CH3)2S
Oxidizing conditions
A. KMnO4 (hot, concentrated)/OH- (or with H3O+)
B. (1) O3
(2) H2O2

8

Free Radical Halogenation
1) Initiation
2) Propagation
3) Termination
Selectivity and stability of radicals (chlorination vs. bromination)

Criteria for Aromatic Compounds
1) cyclic and containing conjugated pi bonds
2) each atom in the ring must have an unhybridized p orbital
3) planar structure
4) delocalization of the pi electrons must lower the electronic energy (4N+2 π electrons)
Antiaromatic compounds satisfy the first 3 rules above but delocalization of the pi electrons increases
the electronic energy (4N π electrons)
Nonaromatic compounds are those that don't satisfy one or more of the first 3 rules above

Side-Chain Reactions of Benzenes
Permanganate Oxidation
O

-

1. KMnO4, OH , boil

OH

+

2. H3O

HO

Chromic acid
(Na2Cr2O7 / H2SO4)
achieves the same
reaction

O

Side-chain Reduction
Clemmenson Reduction – reduces ketones and aldehydes to alkanes
O

Zn (Hg)
HCl, H2O

Wolff Kishner
Reduction does the
same thing with
H2NNH2, OH-, heat

9


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