Alkyl Halides and Elimination Reactions

Flashcards covering the mechanisms, stability, and predictive rules for E1 and E2 elimination reactions from alkyl halides.

Elimination reactions involve the loss of elements from the starting material to form a __________ in the product.

new bond

The removal of the elements of an acid, $HX$, from an organic starting material is specifically called __________.

dehydrohalogenation

Dehydrohalogenation is considered an example of __________ elimination.

$$\beta$$

The most common bases used in dehydrohalogenation are negatively charged oxygen compounds called __________.

alkoxides

In an alkene double bond, each carbon atom is __________ hybridized.

$$sp^2$$

The bond angles of the trigonal planar carbons in an alkene are __________.

$120$ degrees

The double bond of an alkene consists of one $\sigma$ bond and one __________ bond.

$$\pi$$

Due to restricted rotation about double bonds, two stereoisomers of 2-butene, specifically cis and trans, exist as __________.

diastereomers

In general, __________ alkenes are more stable than cis alkenes because the bonded groups are further apart, reducing steric interactions.

trans

The stability of an alkene increases as the number of __________ bonded to the double bond carbons increases.

$R$ groups

Because $sp^2$ carbons have a higher percent s-character than $sp^3$ carbons, they are more able to accept __________ density.

electron

The E2 mechanism is known as __________ elimination.

bimolecular

The E2 mechanism exhibits __________-order kinetics, meaning both the alkyl halide and the base appear in the rate equation.

second

The E2 reaction is __________, meaning all bonds are broken and formed in a single step.

concerted

Strong, sterically hindered nitrogen bases used in E2 reactions include __________ and DBU.

DBN

The rate of an E2 reaction increases as the number of $R$ groups on the carbon with the leaving group increases, because the transition state is stabilized by the partially formed __________.

double bond

The __________ rule predicts that the major product in $\beta$ elimination is the more substituted, and thus more stable, alkene.

Zaitsev

A reaction is __________ when it yields predominantly or exclusively one constitutional isomer when more than one is possible.

regioselective

The E1 mechanism is called __________ elimination and exhibits first-order kinetics.

unimolecular

The slow, rate-determining step of an E1 reaction is the formation of a __________.

carbocation

Unlike E2 reactions which are favored by strong bases, E1 reactions are favored by weaker bases such as __________ and ROH.

$$H_2O$$

The transition state of an E2 reaction requires the four atoms involved to be in a single plane, most often in the __________ periplanar geometry.

anti

In substituted cyclohexanes, E2 elimination must occur from the conformer where the leaving group and the $\beta$ hydrogen are __________ diaxial.

trans

Consecutive elimination reactions are used to produce the two $\pi$ bonds of an __________.

alkyne

The typical strong base used to synthesize alkynes from dihalides is the __________ ion, often used as NaNH2.

amide

Bulky non-nucleophilic bases like $KOC(CH_3)_3$ favor __________ over substitution because they are too hindered to attack a tetravalent carbon.

elimination

Strong nucleophiles that are weak bases, such as $I^-$ or $CN^-$, favor __________ over elimination.

substitution

The E2 reaction is a critical step in the formation of the anti-malarial drug __________.

quinine