Chapter 7 Alkenes and Alkynes 1

Question 1

What are the simplest alkene and alkyne possible?

Answer 1

Simplest alkene: Ethylene

Simplest Alkyne: Acetylene

Question 2

What is the structure in the image?

Answer 2

Ethylene

The simplest alkene

Question 3

What is the molecule in the image?

Answer 3

Propylene OR

1-propene (prop-1-ene)

Question 4

What is the relationship between the two molecules/

Answer 4

Diastereomers

Question 5

What is the difference between the E and Z stereochemistry?

Answer 5

• E: entegegan = opposite
  
  • highest substituents are on opposite sides
• Z: zusammen = Same
  
  • highest substituents are on the same side

Question 6

Are the compounds the same?

Answer 6

No, they are diastereomers and we can differentiate them by using the E and Z nomenclature

Question 7

What is the functional group in the image?

Answer 7

Vinyl group

eg:

Vinyl chloride

(1-chloroethene)

Question 8

What is the functional group in the image?

Provide an example of a compound with the functional group

CH3CH=CH−X

Answer 8

Allyl group or “Propenyl Group”

Eg

Allyl chloride

(3-chloropropene)

Cl—C—C=C

Question 9

What is the functional group in the image?

Provide an example of a compound with the functional group

Answer 9

Benzyl group

eg: Benzyl bromide

6-member benzene with CH₂

Question 10

What is the functional group in the image?

Provide an example of a compound with the functional group

Answer 10

Phenyl group

eg: Phenyl bromide “bromobenzene”

Question 11

What are the four naming rules for alkynes?

Answer 11

1. Find longest chain w/ max number of multiple bonds
2. Number from end to give 1^st multiply bonded position the lowest number
3. Drop “ane” and add “yne”
4. For multiple triple bonds, drop the ne and add diyne, triyne etc

Question 12

What is the compound in the image?

Answer 12

Ethyne

“Acetylene”

Question 13

What are the names of the three compounds?

Are they related?

Answer 13

Propyne

1-butyne

2-butyne

• 1-butyne and 2-butyne are structural isomers

Question 14

What is the name of the compound?

Answer 14

2,4 - Octadiyne

Question 15

What is the name of the compound?

Answer 15

• 13 Carbons = trideca
• triple bond (triyne) on 5, 7, 9
• 3 double bonds (triene) on 1, 3, 11
• 3=4 E (opposite)
• 11=12 E (opposite)

= 3E,11E-trideca-1,3,11-triene-5,7,9-triyne

Question 16

What is the relative polarity of alkanes, alkenes and alkynes?

Answer 16

Alkynes > Alkenes > Alkanes

most polar -> least polar

Question 17

What is the relative acidity of Alkanes, alkenes and alkynes?

Answer 17

Least acidic -> most acidic

Alkane < Alkene < Alkynes

Least polar -> Most polar

Question 18

What three properties are higher in alkynes than in alkenes and alkanes?

Answer 18

Alkynes have a higher boiling point, melting point, and density

Question 19

What is Hydrogenation?

Answer 19

• “add’n of hydrogen to an alkene in presence of metal catalysts to produce alkanes”
• Reaction from the addition of H₂
• Stereospecific
• cis or syn add’n
• Metal catalysts

Question 20

How do catalysts increase the rate of reaction?

Answer 20

Provide a lower energy pathway.

• are not permanently converted to other products

Question 21

What are the relative stabilities of alkenes?

(1-butene vs trans-2-butene vs cis-2-butene)

Answer 21

Trans is most stable and 1-butene (unsubstituted) is the least stable.

Trans-2-butene > Cis-2-butene > 1-butene

Question 22

The ______ on a double bond, the more stable

Answer 22

The more substituents on a double bond, the more stable

Question 23

Why are double bonds with more substituents more stable?

Answer 23

Carbons on a double bond have a partially positive charge which is stabilized by the e- donating effects of alkyl groups

hydrogens are less e- donating= less stable

Question 24

Why are cis alkenes less stable than trans alkenes?

Answer 24

cis alkenes have methyl groups facing the same direction which causes unfavourable steric interactions = decreases stability

Question 25

what is the compound in the image?

Answer 25

Fat: * A triglyceride: triester of glycerol * **polyunsaturated** (\>1 double bond)

Question 26

What is the reaction converting a polyunsaturated triglyceride into a saturated fat?

Answer 26

Hydrogenation of Polyunsaturated triglyceride: * polyunsaturated triglyceride --(H2)/Ni--\> * removes double bonds * saturated fat (triglyceride)

Question 27

What is the compound in the picture?

Answer 27

**Diacetyl** butter flavouring that add yellow colour to margarine IUPAC = butanedione or butane-2,3-dione

Question 28

Why do deuteriums add to the back of steroids in a hydrogenation rxn? (deuteriums are isotope of Hydrogen ²H)

Answer 28

Because of steric hindrance of the nearby methyl group

Question 29

Products: Two possible diastereomers depending on bottom or top addn Bottom: equatorial isopropyl and axial methyl Top: isopropyl and methyl are equatorial

Answer 29

Hydrogenation reaction requiring a metal catalyst and H₂

Question 30

What is halogenation?

Answer 30

Add'n of halogens across a double bond Converts alkene to alkane

Question 31

Halogenation of cyclopentene produces 1:1 racemate of **trans-1,2-dibromocyclopentane** enantiomers (RR; SS) Requires:

Answer 31

Halogenation of cyclopentene requires **Br₂ and achiral solvent** and produces:

Question 32

Halogenation of 1,2-dimethylcyclopentene produces **trans-1,2-Dibromo-1,2-dimethylcyclopentane** And requires: \_\_\_\_

Answer 32

Halogenation of 1,2-dimethylcyclopentene produces **\_\_\_\_\_\_\_\_\_\_\_\_** And requires: **Br₂**

Question 33

What is Markovnikov's Rule?

Answer 33

In an addition reaction, the positive end of an A-B system (eg I-Cl) adds to the least substituted end of the double bond to make the more stable carbocation

Question 34

Which is faster, intermolecular or intramolecular reactions?

Answer 34

Intramolecular reactions are faster: within the same molecule Therefore, intramolecular almost always beats intermolecular reactions

Question 35

What is Zaitsev's rule?

Answer 35

Formation of the more substituted alkene is favored with a small base. * if we use a small base (eg ethoxide or hydroxide) the major product of the rxn will be the more highly substituted alkene (more stable alkene)

Question 36

Whenever an elimination occurs to give the more stable, more highly substituted alkene, chemists say that the elimination follows \_\_\_\_\_\_\_

Answer 36

Whenever an elimination occurs to give the more stable, more highly substituted alkene, chemists say that the elimination follows _Zaitsev's rule_

Question 37

What is kinetic control of product formation?

Answer 37

The preferential formation of one product b/c the free energy of activation leading to its formation is lower than that for another product, and therefore the rate of its formation faster

Question 38

Carrying out dehydrohalogenations with a **bulky base** such as potassium *tert-*butoxide (*t*-BuOK) in *tert*-butyl alcohol (*t-*BuOH) favours the formation of:

Answer 38

Carrying out dehydrohalogenations with a **bulky base** such as potassium *tert-*butoxide (*t*-BuOK) in *tert*-butyl alcohol (*t-*BuOH) favours the formation of _the **less substituted alkene**_

Question 39

When an elimination yields the less substituted alkene, we say that it follows the ________ rule

Answer 39

When an elimination yields the less substituted alkene, we say that it follows the _hofmann_ rule