Chapter 4

Question 1

What are alkenes?

Answer 1

hydrocarbons that contain one or more carbon-carbon double bonds?

Question 2

Size of double bonds?

Answer 2

Double bonds are shorter than single bonds

Question 3

What are stereoisomers?

Answer 3

Same connectivity but a different arrangement in space?

Question 4

What is it called if there are two double bonds?

Answer 4

dienes

Question 5

What is it called if there are three double bonds?

Answer 5

tienes

Question 6

What are constitutional isomers?

Answer 6

Same molecular formula but different connectivities

Question 7

Are constitutional isomers also stereoisomers?

Answer 7

Constitutional isomers are not stereoisomers

Question 8

What is the hybridization of alkene double bond?

Answer 8

Sp2

Question 9

How much s-character does an sp2 orbital have?

Answer 9

33% = s characterr
67% = p character

Question 10

Difference between sp3 and sp2 orbitals?

Answer 10

sp2 = electron density is slightly closer to nucleus
- more s-like character = closer to nucleus

Question 11

What is a pi bond

Answer 11

pi bond = a bond formed by the side overlap of p orbitals

Question 12

are cis and trans stereoisomers or constitutional isomers?

Answer 12

= stereoisomers because connectivities differ in the spatial arrangement of their atoms

Question 13

what are cis-trans stereoisomers?

Answer 13

compounds related by an internal rotation of 180 degree about the double bond

Question 14

alkane vs alkene naming

Answer 14

-ane gets replaced with -ene

Question 15

How to number chain?

Answer 15

When naming an alkene, we find the longest continuous carbon-carbon chain that includes
the double bond. Then number the chain in the direction that gives the double bond the lowest
number, not the branch position.

Question 16

What is a Z stereoisomer?

Answer 16

When atoms of higher atomic number are on the same side of the double bond (also cis)

Question 17

What is an E stereoisomer?

Answer 17

When atoms of higher atomic number are on opposite sides of the double bond (also trans)
- remember E = ears and ears are on opposite sides of your head

Question 18

How to determine if a stereoisomer is cis or trans?

Answer 18

Determine if the higher priority groups are on the same or opposite sides of the double bond

Question 19

Rules of determining if a stereoisomer is cis or trans?

Answer 19

1a. assign higher priority to the group containing the atom of higher atomic number
1b. assign higher priority to the group containing the isotope of higher atomic mass
If nothing is determined to move to 2
2. look at the atoms attached and arrange them in descending priority then make pairwise comparisons
If nothing is selected move to 3
3. look at the next set of atoms attached and arrange them in descending priority then make pairwise comparisons

Question 20

Difference on physical properties of alkanes vs alkenes?

Answer 20

Same physical properties only difference is sp2 vs sp3

Question 21

What determines the relative stability of alkenes?

Answer 21

more stable alkene = lower heat of combustion

Question 22

What determines the heat of combustion?

Answer 22

1. degree of unsaturation : how many R groups are attached to the alkene
2. van der Waals strain : R groups cis to one another are destabilizing

Question 23

Rank the stability of various R - group substitutes.

Answer 23

Tetra-substitutes > Tri-Substitutes > Di-Substitues > Monosubsitues > no subsitutes

Question 24

What are exothermic vs endothermic reactions?

Answer 24

Exothermic = heat in a reaction is liberated or released (- change H)
Endothermic = heat in a reaction is absorbed (+ change H)

Question 25

Which are normally more stable cis or trans stereisomers?

Answer 25

Almost all trans isomers are more stable, due to repulsive forces in cis-isomers

Question 26

What happens when you can shuffle around bonds?

Answer 26

when you can shuffle around bonds = more stable

Question 27

What is Ea

Answer 27

Ea = kinetic term
- How fast
- rate = K [reactant 1] [reactant 2]
* the higher Ea, the slower the rxn
-rate-limiting step is the slow step (bigger hill to go up)

Question 28

What is a catalyst

Answer 28

Catalyst lowers Ea