Ch.7-8 Flashcards
which carbocations have the most stability
3>2>1>methyl
what are some examples of weak bases that are good nucleophiles?
Cl, I, Br, CN, acetate ion
why do rearrangements occur
they occur due to carbocations and are driven by the formation of a more stable carbonation
why are tertiary carbocations more stable than others?
they have a stronger inductive effect due to
What is a 1,2 methyl shift
it is when a methyl group on an adjacent carbon (2 bonds away) shifts to form a more stable carbonation
what type of mechanism will occur with an acid catalyzed dehydration on a tertiary alkyl halide?
an E1 mechanism
in a 1,2 methyl shift, what is moving?
the electrons in the bond connecting the methyl and the carbon are moving towards the positively charged carbonation, the methyl atoms only move as a result of this electron movement
in an acid catalyzed dehydration reaction, what drives the reaction towards a major product?
the formation of the major product is driven by carbonation stability
what is the major product in an alkene formation?
the more stable one, it has lower energy and is thermodynamically favorable to form
how often do rearrangements occur
rearrangements occur very frequently, if there is the possibility for a more stable carbonation, a methyl or hydride shift will occur
what is a 1,2 hydride shift
it is when a hydrogen 2 bonds away from a less stable carbonation shifts towards the positive charge and leads to the formation of a more stable carbonation
how are alkynes formed?
through elimination
what is a gem-dihalide
it is where you have two halogens that are two bonds away from each other (bonded on same carbon)
if you have a gem-dihalide and excess base, what can occur?
you can get the formation of an alkyne through a double dehalogenation
what is a vicinal dihalide
it is a compound that bears two halogens on adjacent carbons (3 bonds away)
What is sodium amide
it is a strong base
what is double dehydrohalogenation
it is a mechanism of a double E2 that forms an alkyne with either a vicinal dihalide or a geminal dihalide
what is an important property of terminal alkynes
they are acidic and can be deprotonated to form a nucleophile that can be used in further mechanisms
what is an alkylation
it is the formation of a new carbon carbon bond
what is the pka of sp, sp2, sp3 and what types of bonds do they represent
sp represents a triple bonded carbon atom and has a pka of 25
sp2 is a double bonded carbon atom that has a pka of 44
sp3 is a single bonded carbon atom that has a pka of 50
to deprotonate a terminal alkyne, what type of reagent do we need?
a strong base like NH2
after deprotonating a terminal alkyne, what is formed?
an electron rich carbanion that can act as a nucleophile in a substitution reaction
what kind of alkyl halide is necessary for a carbanion alkyne to act as a nucleophile
it must be either a primary alkyl halide or a methyl alkylhalide, tertiary and secondary do not work due to the steric effect
if you react a carbanion alkyne with a tertiary or secondary akyl halide, what will occur and what will not occur
we would have an E2 reaction, there would be no new carbon-carbon bond formed (alkylation)
