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University of Santo Tomas
Faculty of Pharmacy
Department of Biochemistry
6. Chapter 6 – Chirality
6.1.
Drawing an Enantiomer
6.2.
Assigning Configuration
6.3.
Determining the Stereoisomeric Relationship between Two Compounds
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6.4.
Identifying Meso Compounds
6.5.
Assigning Configuration from a Fischer Projection
6.6.
Practice Problems
6.6.1.
For each of the following pairs of compounds, determine the relationship between the two compounds:
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7.
Substitution and Elimination Reactions
7.1.
Summary of SN1 and SN2
7.2.
Effects of Protic Solvents and Polar Aprotic Solvent
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7.3.
Review of Concepts
Substitution reactions exchange one functional
group for another.
The electrophile is called the substrate, and it
must contain a leaving group. There are two ways to name halogenated
organic compounds. The systematic name
treats the compound as a
haloalkane, while the common name treats the
compound as an alkyl halide.
The alpha (_) position is the carbon atom
connected directly to the halogen, while the
beta (_) positions are the carbon
atoms connected to the _ position.
Alkyl halides are classified as primary,
secondary, and tertiary according to thenumber of alkyl groups connected to
the _ position.
In a concerted process, nucleophilic attack and
loss of the leaving group occur simultaneously.
In a stepwise process, first the leaving group
leaves, and then the nucleophile attacks.
Evidence for the concerted mechanism, called
SN2, includes the observation of a second-order
rate equation. The SN2 process is said to be
bimolecular.
Methyl halides and primary alkyl halides react
most quickly, while tertiary alkyl halides are
essentially unreactive toward SN2.
When the _ position is a chirality center, the
reaction proceeds with inversion of
configuration. The preference
for back-side attack stems from the need for
constructive overlap of orbitals (according to
MO theory). SN2 reactions
are said to be stereospecific because the
configuration of the product is determined by
the configuration of the
substrate. Evidence for the stepwise mechanism, called
SN1, includes the observation of a first-order
rate equation. These reactions are said to be
unimolecular. • The first step of an SN1 process
(loss of a leaving group) is the rate-determining
step.
The carbocation intermediate can be attacked
from either side, leading to inversion of
configuration and retention of configuration.
There is usually a slight preference for the
inversion product due to the formation of ion
pairs.
A proton transfer is necessary at the beginning
of an SN1 mechanism if the substrate is an
alcohol.
A carbocation rearrangement can take place if
it will lead to a more stable carbocation
intermediate.
A proton transfer is necessary at the end of an
SN1 mechanism if the nucleophile is neutral
(not negatively charged).
When the solvent functions as a nucleophile,
the reaction is called a solvolysis reaction.
A proton transfer is necessary at the beginning
of an SN2 mechanism if the leaving group is an
OH group.
A proton transfer must occur at the end of an
SN2 mechanism if the nucleophile is neutral.
There are four factors that impact the
competition between the SN2 mechanism and
SN1: (1) the substrate, (2) the nucleophile, (3)
the leaving group, and (4) the solvent.
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The most common leaving groups are halides
and sulfonate ions. Of the sulfonate ions, the
most common is the tosylate group.
Protic solvents favor SN1, while polar aprotic
solvents favor SN2.
Depending on the type of nucleophile used,
substitution reactions can be used to produce a
wide range of different compounds.
7.4.
Possible substitution reactions
7.5.
Summary of Reactions
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7.6.
Guidelines for Determining the Regiochemical and Sterochemical Outcome of Substitution and Elimination
Reactions
7.7.
Predicting the Regiochemical Outcome of an E2 Reaction
7.8.
Predicting the Stereochemical Outcome of an E2 Reaction
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Addition Reactions
Practice Problems
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8.
Chapter 7 – Alkyl Halides
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Drawing Resonance Structures of Radicals
Identifying the Weakest C—H Bond in a compound
Predicting the selectivity of radical bromination
Predicting the stereochemical outcome of radical bromination
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Predicting the products of allylic bromination
Predicting the products for radical addition of HBr
Functional Group Transformation
The outcomes can be manipulated by using specific solvents/reagents.
ALCOHOLS AND PHENOLS
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Map of reactions for interconversion between alkanes, alkenes, alkynes, alkyl halides, alcohols, and ketones/aldehydes.
Grignard Reagent
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Review of Reactions
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Thiols and Ethers
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ALDEHYDES AND KETONES
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CARBOXYLIC ACID AND DERIVATIVES
Reactivity of Derivatives: Left to right, most reactive to least reactive
SUMMARY
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