Chapter 6 Flashcards
The chemistry of vinyl and aryl halides is different from that of alkyl halides because of their _______ and _______
bonding and hybridization
halogens are more _______ than carbon, making the C-X bond _______
electronegative
polar
For common (“trivial”) name as alkyl halide
1) name the _______ group
2) name the _______
alkyl
halide
_______ dihalide: two halogen atoms are bonded to the same carbon
geminal
______________ dihalide: two halogen atoms are bonded to adjacent carbons
vicinal
the larger the surface area of an alkyl halide, the _______ the boiling point
- Larger _______ take priority
higher
halogen
alkyl flourides and chlorides are _______ dense than water, so in bilayer it will occupy the _______ layer
less
top
alkyl chlorides with 2 or more Cl atoms are _______ dense than water, so in bilayer it will occupy the _______ layer
more
bottom
all alkyl bromides and iodides are _______ dense than water
more
What are the 2 types of substitution reactions?
1) bonds broken and formed at the same time (Sn2)
2) old bond breaks, then new bond forms (Sn1)
bimolecular nucleophilic substitution (_______) have __ molecules in r.d.s
Sn2
2
Sn2 reactions are ___-step reactions, where the bond is broken and formed _______
1
simultaneously (concerted)
What type of intermediate is present in the SN2 reaction of cyanide with bromoethane?
there is no intermediate
What are the 3 options that could result from attack at the chiral electrophilic carbon
1) retention
2) inversion
3) racemization
Sn2 reactions occur with 100% _______ of configuration at the electrophilic carbon. This is a _______ reaction
inversion
stereospecific
to form a new bond, the _______ must approach the electrophilic C from the side that is _______ of the leaving group. This is called a _______
nucleophile
opposite
backside attack
The best leaving groups are
1) _______: strong EN creates a partial positive on carbon
2) stable:
3) polarizable:
1) electron-withdrawing
2) should be weak bases (conjugate bases of strong acids)
3) maintain partial bonding with the carbon atom in the TS
What is the most common leaving group that we will see in Sn2 reactions?
sulfonate
different alkyl halides undergo Sn2 reactions at different rates:
1) place your focus on the carbon attached to the leaving group, this is the _______ C
2) _______ hindrance plays a large role in the rate of Sn2 reactions
electrophilic
steric
________ stabilizes the transition state which results in the _______ of the rate
resonance
increase
Sn1 reactions have ___ molecule in r.d.s
1
The rate of Sn1 reactions are completely dependant on the concentration of the _______
electrophile
SN1 reactions are ___-step reaction where the old bond is broken first and then the new bond is formed
2
What are the steps to an Sn1 reaction?
1) LG leaves
2) nucleophile attacks carbocation
3) solvent attacks new positive charge
The rate-limiting step of the Sn1 reaction is ionization to form a carbocation which is an extremely _______ process
endothermic
Hammonds postulate: the structure of the transition state most resembles the species to which it is closest in _______
energy
rates of Sn1 reactions depend strongly on _______ stability
- then depends on _______
carbocation
leaving group
rank 1°, 2°, and 3° and their allylic and benzylics for Sn1 rates
3°allylic and benzylic > 3°, 2° allylic and benzylic > 2°, 1° allylic and benzylic > 1°
In the Sn1 mechanism, the carbocation formed is _______ and _______
planar
achiral
Sn1: attack from both faces gives _______ enantiomers of the product
50% retention
50% inversion
racemic mixture
- little more inversion
Trends in nucleophiles (Sn2):
1) when comparing charged vs neutral, _______ is stronger
2) nucleophilicity _______ from left to right in the periodic table
3) in the same group (column), nucleophilicity _______ as you move down
4) bulky groups _______ nucleophilicity due to their steric hindrance
1) charged
2) decreases
3) increases
4) decrease
more EN atoms have more tight held nonbonding electrons that are _______ reactive toward forming new bonds
less
Solvent: a liquid that can dissolve the _______. It interacts with reactants, products, and intermediates during the reaction process
reactants
What are the 2 main types of solvents?
1) polar protic (p/p)
- SN1
2) polar aprotic
- SN2
_______ solvents have acidic hydrogens (O-H and N-H) that can solvate the nucleophile, reducing their nucleophilicity
polar protic (p/p)
_______ solvents do not have acidic protons and cannot hydrogen bond
polar aprotic
What is one example of a polar protic solvent?
EtOH or H2O
What is one example of a polar aprotic solvent?
THF or diethyl ether
Carbocations (C+) frequently undergo structural changes called rearrangements to form more stable ions when possible. What are the 2 different rearrangements?
1) hydride shift
2) alkyl shift
In Hydride shift, you can _______ make the C+ worse or same, you have to make it _______
never
better
In Alkyl shift, an ________ group can rearrange to make the carbocation more stable
alkyl
What are the steps to ring expansion?
1) check carbocation to see if you can relieve ring strain
2) then look at C+ stability
- Ring strain trumps C+ stability
_______: both nucleophile and electrophile within the same molecule
intramolecular
When you have an intramolecular molecule, what are you allowed to do to the molecule?
cyclizations or ring formation
