7. Reaction of Alkyl halide Flashcards
Reactions of Alkyl halide involves
Substitution
Reaction
Nucleophilic Reactions
-Nucleophilic Substitution Bimolecular (SN2)
Nucleophilic Substitution Unimolecular (SN1)
Substitution
Reaction
Any atom on the alkyl halide is
replaced with another group. T or F
False. HALOGEN atom on the alkyl halide is
replaced with another group
Halogen is more electronegative
than carbon, the C-X bond breaks
heterolytically and X- leaves. T or F?
True. The group replacing X- is a NUCLROPHILE
Nucleophilic Substitution Bimolecular (SN2) is dependent on?
Dependent on the CONCENTRATION (M) of the TWO REACTANTS - Reaction Rate = k[A][B]
Nucleophilic Substitution Bimolecular (SN2) has how many steps?
single-step thus, there is no intermediates
Nucleophilic Substitution Bimolecular (SN2) configuration of reactant and products?
Product has the PPOSITE configuration of the
reactant. Due to the attack at the opposite of the halogen or leaving group.
SN2 Mechanism: Factors
Affecting the Rate
- Substrate
- Nucleophile
- Leaving Group
- Solvent
Substrate must be sterically hindered substrate, the
faster reaction. T or F?
Substrate must be LESS sterically hindered substrate, the faster reaction
Nucleophilicity of a molecule
depends on the substrate, solvent and reactant
concentrations.
True. SN2 mechanism depends on the concentration of all reactants.
Best leaving groups are those that cannot stabilize
the negative charge in the transition state. T or F?
Best leaving groups are those that BEST stabilize
the negative charge in the TRANSITION STATE as an effect,
there will be faster reaction.
Ideally, weakest bases
Polar protic solvents, which are polar and contains –OH or –NH group are the best in SN2 mechanism
polar APROTIC solvents, which are polar but DO NOT HAVE –OH or –NH group are the best in SN2 mechanism
Nucleophilic Substitution Unimolecular (SN1) is dependent only on?
Rate is dependent only on the substrate (alkyl halide) and independent of the nucleophile
concentration
Rate = k[A]
Nucleophilic Substitution Unimolecular (SN1) has how many steps?
Two. Involve formation of carbocation intermediate followed by the losing of proton.
Nucleophilic Substitution Unimolecular (SN1) has what configuration in reactant and product.
Product is
optically active
because 50:50
mixture of +/- results. RACEMIC
Factors
Affecting the Rate of SN1 Mechanism in the substrate?
Stability of the carbocation greatly favors the
reaction. Must have a reactive halides
Factors
Affecting the Rate of SN1 Mechanism in the leaving group.
most stable, best leaving group
Factors
Affecting the Rate of SN1 Mechanism in the Nucleophile: Affects the reaction rate. T or F?
False. DOES NOT affect reaction rate because SN1 is substrate concentration dependent.
BUT it must be non basic to prevent a
competitive elimination of HX
Factors
Affecting the Rate of SN1 Mechanism in the Solvent: effect is due to stabilization or destabilization of the
transition state T or F?
What solvent is best?
True.
Polar protic solvent is highly favored in this reaction. Contains OH and NH2
Elimination Reactions types:
- Elimination Unimolecular (E1)
- Elimination Bimolecular (E2)
- Periplanar Geometry - Elimination unimolecular conjugate base (E1cB)
Elimination Unimolecular (E1) is similar so SN1 and follows what rule in formation of products?
More stable product is formed
(Zaitsev’s rule) and follows a 1st order kinetics
- Geometrical requirement isn’t
required
Elimination Bimolecular (E2)
C-H and C-X bonds
do not break simultaneously, giving the alkene in a two step
process.
C-H and C-X bonds
break SIMULTANEOUSLY giving the alkene in a SINGLE
process. Similar to SN2.
Elimination unimolecular conjugate base (E1cB)
C-H bond breaks first giving a carbanion intermediate
that loses –X giving the alkene. T or F?
True. This usually occur in biological reactions
Elimination unimolecular conjugate base (E1cB) is common to what substrates?
substrates with POOR LEAVING GROUP
such as –OH, two carbons removed from a carbonyl
group, as in HO-C-CH-C=O
