Alkyl Halides Flashcards
Reactivity of alkyl halides depend on
Bond energy, polarity (more = more reactive) and bond length
What is the hybridization of alkyl halides?
sp3
C-Cl bond length in alkyl halide
178 pm
Alkyl halide bond angle
109.5º
Down the group, H-X reactivity
Increases
H-X reactivity order
HI > HBr > HCl > HF
The __ -carbon of alkyl halides is _____philic in nature
alpha-carbon is electrophilic in nature
Halogen atom is a good __________ group
Leaving group
The elimination reaction (dehydrohalogenation) of an alkyl halide gives an
Alkene
The bond energy of HI is
228 kJ/mol
The molecule undergoing nucleophilic reaction is called the
Substrate
The group leaving the substrate/being replaced is called the
Nucleofuge
Any species ________ or ___________ with an unshared pair of e- can act both as a base and a nucleophile
Neutral or negatively charged
A nucleophile undergoes _________________ reactions
Nucleophilic substitution or addition reactions
Bases give __________ reactions
Elimination reactions
The positive carbon of alkyl carbocation is ____ hybridized and therefore has a __________ structure
sp2 and trigonal planar structure
Alkyl groups are electron _______
Donating
Carbocation stability order
Tertiary carbocation > Secondary carbocation > Primary carbocation > Methyl carbocation
(Most stable) (Least stable)
Unimolecular substitution is ______ and _____ step mechanism
Unimolecular and two step mechanism
SN1: First step is
Slow / rate determining
SN1 mechanism is followed by
Tertiary alkyl halides
SN1 mechanism is favored by ______ solvents (having _______ bonds)
Highly ionizing polar solvents (Polar protic). (having O-H , N-H bonds)
SN1 has ______ nucleophile and _____ leaving group
Weak nucleophile and good leaving group
SN1 follow _____ order kinetics
First order kinetics
If nucleophile attacks carbocation from the side of the leaving group, the product shows _______ of configuration.
If nucleophile attacks carbocation from the opposite side, the product shows _______ of configuration.
Side = Retention
Opposite = Inversion (O and I are both vowels)
Racemic Mixture is
When reactant is chiral, so a mixture of two enantiomers are produced
Racemization is
A mixture of retention and inversion
In SN1 there is _______ racemization
Partial
In SN1 there is more _______ than ________
Inversion than retention (more opps in SN1)
SN2 is _____ and ___ step
Bimolecular and one step
SN2 is followed by ________
Primary carbocations and methyl halides
SN2 follows _____ order kinetics
Second order kinetics
SN2 is favored by _________ solvents
Polar aprotic solvents (aprotic means unable to ionize)
SN2 goes thru _______ of configuration
Inversion only
Secondary alkyl halides follow SN1 if __________, and SN2 if _______
SN1 if polar protic solvent present, SN2 if polar aprotic solvent present
In 1,2 elimination, proton is removed from ___ position and halide is removed from ____ position
Proton from Beta, Halide from Alpha position
SN2 has a ____ nucleophile and a ____ leaving group
Strong nucleophile and bad leaving group
Which leaves first in 1,2 elimination
Beta first then alpha
E1 is ____ and _______
Unimolecular and two steps
E1 is followed by _____ alkyl halides
Tertiary
E1 follows _____ order kinetics
First
E1 has a ____ base
Weak base
E1 needs _______ solvents
Polar protic solvents
E2 is ___ and _____ step
Bimolecular and one step
E2 follows ___ order kinetics
Second
E2 prefers ______ solvents
Polar aprotic solvents
E2 has a _____ base
Strong base
E2 is followed by _____ alkyl halides
Primary
Crowding around alpha carbocation generally favors _____ over _______. This is due to _______
Elimination over substitution. This is due to greater steric hindrance
The greater number of alkyl groups favors _____ over ______
Elimination over substitution
A stronger base will favor _____ and a stronger nucleophile will favor _______
Base will favor elimination and nucleophile will favor substitution
2bromo propane with ethoxide ion (C2H5O-) vs with ethanthiolate ion (C2H5S-)
Ethoxide ion = Elimination
Ethanthiolate ion = Substitution
Order from strongest nucelophiles to strongest bases
I-, HS-, RS- > Br-, OH-, OR-, CH- > Cl, F, NH3, RCOO- > H2O, ROH
Strongest Weakest (but Strongest
Nucleophile Nucleophile Base)