Chapter 4

Question 1

Describe the structure of Alkenes

Answer 1

The two carbon atoms of the double bond and the four atoms bonded to them line in a plane, with bond angles of roughly 120

Question 2

According to the orbital overlap model, a double bond consists of one _______ bond formed by the overlap of sp2 hybridized orbitals AND one _______ formed by the overlap of parallel 2p orbitals

Answer 2

σ
π

Question 3

If you rotate about a π bond, it does what? What does this restriction mean for C-C conformations?

Answer 3

Rotation removes the overlap in the 2p orbitals thus breaking the π bond. Because of restricted rotation about a C-C double bond, groups on the carbons of a double bond are either cis or trans isomers to each other, not staggered or eclipsed conformations

Question 4

Is the cis or trans conformation around a C=C bond in an alkene more stable?

Answer 4

Due to the nonbonding interaction strain (steric) between alkyl (heavy) groups on the same side of the double bond, a trans alkene is more stable than an isomeric cis alkene

Question 5

Compare usage of the cis-trans system and E-Z system for determining alkene configurations

Answer 5

The cis-trans system is generally suitable for alkenes with one non-hydrogen group attached to each of the C=C carbons

The E-Z system is suitable for all alkenes, including those with 3 or four non-hydrogen groups.

Question 6

Draw trans-3-hexene and cis-3,4-dimethyl-2-pentene, which would be E and which would be Z?

Answer 6

Question 7

What is the different between a Z (zusammen) and E (entgegen) configuration? Which one is “cis” and which is “trans”?

Answer 7

Question 8

To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the first priority rule?

Answer 8

“how chilly the nights, oh such clear bright ice!”

Question 9

To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the second priority rule if the bonded atoms are all of similar atomic number?

Answer 9

Question 10

To determine if a group on a C=C bond is higher or lower, it is assigned a priority. What is the third priority rule (HINT) it does not related to ranking but is related to the kinds of bonds present

Answer 10

Question 11

The configuration of the double bond in cyclo________ through cyclo_________ MUST be ________.

Answer 11

Propene
Heptene
Cis
These rings are not large enough to accommodate a trans double bond

Question 12

__________ is the smallest cycloalkene that can accommodate a trans double bond

Answer 12

Cyclooctene

Question 13

For an alkene with n C=C bonds that can show cis-trans isomerism, ________ cis-trans isomers are possible

Answer 13

2ⁿ

Question 14

Draw trans,trans-2,4-Heptadiene
Draw trans,cis-2,4-Heptadiene

Answer 14

Question 15

[IUPAC] use the infix _______ to show the presence of a C=C bond. Number the parent chain to give the first C of the double bond the _________ number.

Answer 15

-en-
lower

Question 16

[IUPAC] For a cycloalkene, number the atoms in the ring beginning with . . .

Answer 16

the two carbons of the double bond

Question 17

[IUPAC] When naming alkenes, the parent chain is the longest chain . . .

Answer 17

containing the entire C=C bond EVEN IF a different chain with NO C=C is longer

Question 18

[IUPAC] Name the following.

Answer 18

1-hexene
4-methyl-1-hexene
2-ethyl-3-methyl-1-pentene

Question 19

[IUPAC] The presence of multiple double bonds is indicated by . . .

Answer 19

The appropriate suffix (-diene, -triene) and associated location number

Question 20

[IUPAC] Name the following.

Answer 20

2-pentene
2-methyl-3-hexene

Question 21

[IUPAC] Name the following.

Answer 21

3-ethyl-1-butene
5-methyl-1,3-hexadiene

Question 22

[IUPAC] use the infix _______ to show the presence of a C≡C bond. Number the parent chain to give the first C of the triple bond the _________ number.

Answer 22

-yne-
lower

Question 23

[IUPAC] Name the following.

Answer 23

3-methyl-1-butyne
6,6-dimethyl-3-heptyne

Question 24

The functional group of an alkyne is a ________. Consisting of . . . ?

Answer 24

C≡C triple bond
- one σ bond between overlapping sp orbitals
- 2 π bonds formed by overlap of sets of parallel 2p orbitals

Question 25

Alkenes and Alkynes are ________ compounds. The only attractive forces between their molecules are ____________

Answer 25

nonpolar dispersion forces

Question 26

Alkenes/Alkynes that are liquid at room temperature are _____ dense than water. They are _______ in water.

Answer 26

less insoluble

Question 27

Since s orbitals are closer to the nucleus than p orbitals, s orbitals hold a ______ charger better. Thus, sp carbon is ________ electronegative than sp2 carbon, which is _______ electronegative than sp3 carbon

Answer 27

negative more more

Question 28

Rank ethane, ethylene, and acetylene by increasing acidity based on how the % s character impacts conjugate stability

Answer 28

Question 29

For carbocations, the electron density of the carbon bearing the negative charge ___________ as its hybridization changes from sp3 -> sp2 -> sp and electronegativity ___________

Answer 29

decreases increases

Question 30

The ______ the e- density of a carbocation, the ______ stable the compound.

Answer 30

lower more

Question 31

What is the major difference between the chemistry of Alkenes and Alkynes which interacting with strong bases?

Answer 31

The H atom of a *terminal alkyne* is sufficiently acidic (low pKa) that it can be removed by a strong base to create an alkyne anion

Question 32

Keq = __________ pKa1 is ALWAYS the _______ acid, meaning its _____ in value

Answer 32

Keq = 10^{pKa2 - pKa1} stronger acid, lower