Alkenes and Alkynes reactions

Question 1

Double bond equivalent

Answer 1

• All double bonds
• All the cycles
• Double bond equal to 2

Question 2

Elements of unsaturation

Answer 2

• Unsaturated. Capable of adding hydrogens in the presence of a catalyst to form a saturated alkane

Question 3

Configurational Isomer

Answer 3

• Rotation about the double bond could potentially generate conformational isomer
• This cannot happen. Rotation would break the (strong) double bond between the carbon atoms

Question 4

Cis trans

Answer 4

• Only applies when both ends of the double bond have two
• Different groups attached, but groups at one end of double bond are identical to those at the other

Question 5

Elimination reaction

Answer 5

• Loss of two atoms or groups from the substrate, usually with formation of a new pi bond
• Carbon carbon double bond proton and a halide ion is called dehydrohalogenation, and the product is an alkene
• substitutions (SN1 and SN2) and both unimolecular or biomolecular

Question 6

Substitution

Answer 6

• Sn1 and Sn2 substitution unimolecular and bimolecular

Question 7

E1 reaction

Answer 7

• Unimolecular ionisation to give a carbocation instead of collision of 2 - curly arrow from carbon with halide to halide
• Deprotonation by a weak base
• Alcohol and water are good ionising solvents
• Without strong base force E2

Question 8

Alkenes

Answer 8

• Hydrocarbons with carbon–carbon double bonds, sometimes called olefins
• relatively reactive, considered as a functional group
  Alkenes 2 sp2 hybridised carbons, trigonal planar geometry

Question 9

E/Z nomenclature

Answer 9

• Must be used when we have completely different groups at the two ends of the double bond check priority of groups
• E is on the opposite and z is on the same side

Question 10

Competition between E1 and SN1

Answer 10

• Ionisation to form a carbocation carbon curly arrow to halide
• Removal of halide forms positve cation
• Nucleophilic attack by the solvent on the carbocation

Question 11

Rearrangement in E1 reaction

Answer 11

• E1 may be accompanied by rearrangements such as hydride shifts and alkyl shifts
• Ionisation to form a carbocation
• A hydride shift forms a more stable carbocation
• The weakly basic solvent removes either adjacent proton

Question 12

Zaitsev’s Rule

Answer 12

• In elimination reactions, the most substituted alkene usually predominates
• The more methyl groups takes priority most substituted carbon

Question 13

Rearrangement in E1 and Zaitsev’s Rule

Answer 13

• In ethanol 3 elimination products are formed
• This secondary carbocation can lose a proton to give an unrearranged alkene

Question 14

E2 reaction

Answer 14

• Rate-limiting transition state involves two molecules
• can be a strong base as well as a strong nucleophile, but react as base
• Mechanism is blocked because the tertiary alkyl halide is too hindered for Sn2

Question 15

Reaction of alkyl halides E2

Answer 15

3° > 2° > 1°. Reflects the greater
stability of highly substituted double bonds follows Zaitsev rule - most substituted not favoured
- Having bulky base favours E2 over Sn2

Question 16

Strong

Predicting product from base

Answer 16

Alkyl halide with a strong base form Sn2 and E2

Question 17

Weak

Predicting product from base

Answer 17

Alkyl halide with a weak base form Sn1 and E1

Question 18

Primary alkyl halide with strong base

Answer 18

• Reactants of typical E2 reaction

Question 19

Secondary alkyl halide with strong base

Answer 19

• Can be E2 or Sn2

Question 20

Secondary alkyl halide and weak base

Answer 20

• SN1 and E1 slow

Question 21

Tertiary alkyl halide and strong base

Answer 21

• E2 reaction only able to occour due to steric hinderance

Question 22

Tertiary alkyl halide and weak base

Answer 22

• E1 and E2 reactions

Question 23

Hydration reaction

Answer 23

• Add strong acid to the alcohol
• Protonation of the alcohol forming H2O
• Now good leaving group ionisation to form carbon cation
• final hydrogen is then extracted by water

Question 24

Alkene reactions

Answer 24

• Removal of the pi bond
• Strong electrophile pulls the electron away then carboncation is attacked by a nucleophile through electrophilic addition

Question 25

Dehydration reaction

Answer 25

• Attack of pi bond on electrophile
• Attack you nucleophile gives additional product

Question 26

Markonikov rule

Answer 26

• Addition of proton acid to carbon atom that holds the greatest number of hydrogen atoms
• More stable intermediate carbocation

Question 27

Alkene to alcohol

Answer 27

• Protonation of double bond forms carbon cation
• Nucleophilic attack of water gives protonated alcohol
• Deprotonation of alcohol

Question 28

Addition of halogen to alkene

Answer 28

• Halogen molecule is an electrophile
• Halide ion open up the halonium ion forms vicinal dihalides

Question 29

Hydrogenation alkene reagent

Answer 29

• Ni & Pt and H2

Question 30

Dihydroxylation of alkene

Answer 30

• Addition of Potassium permanganate for 2 alcohol

Question 31

Oximercutration

Answer 31

Use the mercuary reagent hydrates the alkene by

Question 32

Oximercutration

Answer 32

Use the mercuary reagent hydrates the alkene by

Question 33

Hydroboration–oxidation

Answer 33

• hydrating an alkene with anti-Markovnikov orientation
• Reagent Boron BH3 THF

Question 34

Alkyne

Answer 34

• Hydrocarbons with triple bond acetylenes
• 2 elements of unsaturation double bond equivelent
• 1sp bond and 2 pi bonds

Question 35

Reactions with Alkynes

Answer 35

• Terminal alkynes more acidic proton that can be pulled by strong base
• Deprotonation of terminal acetylenes form carbon cations called acetylide ions
• Substitute acetylene via SN2 reaction (Must not be bulky so primary alkyl halide)

Question 36

Addition to carbonyl group

Answer 36

• Oxygen is more electronegative compared carbon there carbon is electrophilic
• Aceylide ion attacks the carbonyl forming an alkoxide ion which is a strong base
• Addition of diluted acid H3O arrow from O to H3O forms an alcohol

Question 37

Reduction of alkynes

Answer 37

• Platinum reagent used almost imposible to just reduce to only alkene so turns to alkane