Chapter 6 - Organic Halogen Compounds Flashcards
Alkyl halides undergo what reaction?
Nucleophilic substitution reactions
Reaction in which a nucleophile displaces the halide leaving group from the alkyl halide substrate.
Nucleophilic substitution reactions
Why nucleophilic substitution reversible?
because the leaving group also has an unshared electron pair
What are the most common nucleophiles? (5)
oxygen, nitrogen, sulfur, halogen, and carbon nucleophiles
Two main nucleophilic substitution mechanisms
Sn2 and Sn1
A one-step process in which the bond to the leaving group begins to break as the bond to the nucleophile begins to form
Sn2 mechanism
3 steps of Sn2 mechanism
- Backside attack
- Both partly bonded
- the nucleophile supplies another electron pair to the carbon atom as the leaving group departs
What molecules are involved in the key step of Sn2? (2)
- Nucleophile
- Substrate
True or False:
Every SN2 displacement occurs with inversion of
configuration.
True
True or False:
The reaction is fastest when the alkyl group of the substrate is methyl or primary and
Slowest (usually not at all) when it is tertiary.
True
a two-step process where the bond between the carbon and the leaving group breaks first and then the resulting carbocation combines with the nucleophile.
Sn1 mechanism
Sn1 mechanism involves this reactant
Substrate only
True or False:
The rate of the reaction does depend on the concentration of the nucleophile in Sn1 mechanism.
False
(Does not depend)
When is Sn1 reaction fastest?
when the alkyl group of the substrate is tertiary
When is Sn1 slowest?
when the alkyl group of the substrate is primary
These are solvents such as water or alcohols that can donate protons
Polar protic solvents
These are solvents such as acetone, dimethyl sulfoxide that cannot donate protons
Polar aprotic solvents
True or False:
If the nucleophile is weak, the SN2 mechanism will be favored
False
(If the nucleophile is strong)
Mechanism where a hydrogen atom and a halogen atom from adjacent carbons are eliminated and a carbon–carbon double bond is formed.
Elimination (or dehydrohalogenation)
A one step process where HX is eliminated and a C=C bond is formed in the same step
E2 mechanism
A two-step process and has the same first step as the SN1 mechanism
E1 mechanism
In tertiary halides, substitution can only occur by what mechanism?
SN1 mechanism
In tertiary halides, elimination can occur by what mechanism?
E1 or E2 mechanism
True or False:
With weak nucleophiles and polar solvents - the SN1 and E1 mechanisms compete with each other
True
Only possible mechanism in primary halides (2)
SN2 and E2 mechanisms
What reactions are possible in secondary halides?
SN2, SN1, E2, E1
Compounds used in dry cleaning and as degreasing agents in metal and textile processing (2)
Trichloroethylenes and tetrachloroethylenes
are polyhalogenated compounds containing chlorine and fluorine.
Chlorofluorocarbons
