Alkenes and Alkynes (copy)

LEC

distillation

cis-trans isomers of alkenes are configurational stereoisomers that can be separated from one another by what process? (taking advantage of the difference in their boiling points)

light or heat

the required energy to break the pi bond in geometric isomers of alkenes may be in the form of (?)

no

does the conversion of cis to trans occur under normal laboratory conditions?

addition reaction

• the most common reaction with alkenes

• this process is product-favored because the products are more stable (sigma bonded)

Includes:

• Halogenation

• Hydration

• Hydrohalogenation

acid catalyst

if this is present in hydration, water adds to alkenes, and the products are alcohols

acids

various (?) can add to double bonds of alkanes

unsymmetric

if both the reagent and the alkene are (?), 2 products are possible

regioisomers

a class of constitutional isomers which have the same functional groups but attached at different positions

regiospecific additions

produce only 1 regioisomer

regioselective additions

one major regioisomer is produced, while the other is present in only trace amounts

Markovnikov’s Rule

When an unsymmetric reagent is added to an unsymmetric alkene, the electropositive part of the reagent bonds to the carbon of the double bond that has the greater number of hydrogen atoms attached, or the more electronegative part of the reagent bonds to the carbon of the double bond that is more substituted (less hydrogen)

electrophilic addition

A reaction in which an electrophile is added to an alkene

electrophiles

“electron lovers”

• Electron-poor reagents

• Seeks electrons

• e.g. often cations, electron-deficient

  species, Lewis acids

nucleophiles

“nucleus lovers”

• Electron-rich reagents

• form bonds by donating electrons to an electrophile

• e.g. electronegative elements, Lewis bases, negatively-charged species, has multiple bonds

nucleophile

the (?) can act as a supplier of pi electrons to (?)

nucleophile

in the electrophilic addition of alkenes, the C=C double bond acts as a (?) due to its pi electrons

proton (H+)

what serves as the attacking electrophile?

2

in the Mechanism of Electrophilic Addition of Alkenes, as the proton approaches the pi bond, (?) pi electrons form a sigma bond between the proton and one carbon atom

unstable and reactive

carbocations are highly (?) because there are only six electrons around the positively- charged carbon (NOT OCTET)

increases

Carbocation stability (?) as the number of adjacent alkyl groups increases.

inductive effects

(an explanation for carbocation stabilization)

an alkyl group can share electron density with an adjacent carbocation, therby stabilizing it

hyperconjugation

(an explanation for carbocation stabilization)

• electrons in the C-H bonds of adjacent carbon atoms can overlap with the empty p-orbital of the carbocation (as long as they are planar)

stabilizing

the interaction between a bonding orbital and an empty p-orbital is (?)

alkyl halide

what is the product of hydrohalogenation?

alcohol

what is the product of the hydration mechanism?

pi bonds

halogens react with what bonds due to their polarizability?

vicinal dihalide

what is the product of the halogenation of alkenes?

hydroboration

the addition of borane (BH3) to an alkene, forming alkylborane

less

in hydroboration (unsymmetrical alkenes), the boron atom bonds to the (?) substituted carbon atom

alcohol

what is the product of the hydroboration-oxidation of alkenes?

metal catalyst

in the reduction of alkenes, the addition of H2 occurs only in the presence of a (?)

conjugated diene

(type of diene)

• double bonds are separated by one single bond

• sometimes called as 1,3-dienes

• 1,3-butadiene is the simplest

isolated diene

(type of diene)

• double bonds are separated by more than one single bond

cumulated diene

(type of diene)

• double bonds are adjacent

allylic carbocation

A carbocation with a carbon-carbon double bond adjacent to the positive carbon

concerted reaction

a reaction in which all bond-breaking and bond-making occur at the same time

diels-alder reaction

the reaction between a conjugated diene and an alkene (dienophile) to form unsaturated six-membered rings

dicarbonyl compound

for a cycloalkene, oxidative cleavage results in a single molecule with 2 carbonyl groups, or a (?)

epoxide

• cyclic ether with a three-membered ring

• contains an oxygen atom attached to two adjacent carbon atoms of a hydrocarbon

terminal alkyne

alkyne that has at least one hydrogen atom directly bonded to each of the carbon atoms involved in the triple bond

• require the presence of an additional Hg2+ catalyst (usually HgSO4) to yield methyl ketone by Markovnikov's addition of water

internal alkyne

alkyne that has no hydrogen atoms directly bonded to either of the carbon atoms involved in the triple bond

• undergo hydration with a concentration sulfuric acid to form ketones

vinyl halide

Has a halogen atom directly attached to a carbon atom within a carbon-carbon double bond (C=C)

• addition of one mole

geminal dihalide

has 2 halogen atoms directly attached to the same carbon atom

• vinyl halide reacts with a second mole of HX to form this

sp hybridized C—H bonds

what is the most acidic among sp, sp2, and sp3 hybridized C—H bonds?

strong base

terminal alkynes are readily deprotonated with (?) in a Bronsted-Lowry acid-base reaction

acetylide ion

resulting ion from the deprotonation of terminal alkynes with a sufficiently strong base

• they can react with a variety of electrophiles