Chapter 4

Question 1

Define saturated hydrocarbon

Answer 1

Hydrocarbons that contain only single bonds between carbon atoms.

• Simplest form of hydrocarbons
• Saturated bc each carbon atom is bonded to as many hydrogen atoms as possible

Question 2

Define alkane

Answer 2

saturated hydrogen carbons with sigma (single bonds)

• can be in a chain or ring

Question 3

What are the two types of alkanes?

Answer 3

Acyclic alkanes and cycloalkanes

Question 4

Define acyclic alkanes

Answer 4

Formula= CnH2n+2

Linear and branched chains

• saturated hydrocarbon bc max number of hydrogens

Question 5

Define cycloalkanes

Answer 5

Formula = CnH2n

• Makes a ring
• have 2 fewer Hydrogens than acyclic

Question 6

What is an alkane’s hybridization?

Answer 6

Sp3 and tetrahedral geometry

Question 7

Define isomers

Answer 7

Two different compounds with the same molecular formula

Question 8

What are the two main types of isomers?

Answer 8

Constitutional isomers and stereoisomers

Question 9

Define constitutional isomers

Answer 9

molecules that differ in the way the atoms are connected to each other

Question 10

Define alkyl group

Answer 10

Formed by removing one hydrogen from an alkane

Question 11

Are alkanes polar or nonpolar?

Answer 11

Nonpolar

• they only have c-c and c-h bonds

Question 12

Do alkanes have lower or higher mp’s and bp’s than more polar compounds?

Answer 12

Lower mp and bp bc of less intermolecular forces

Question 13

How does the mp and bp in alkanes increase?

Answer 13

Increasing the number of carbons increases surface area which increases mp and bp

Question 14

Does branching on isomers increase or decrease bp?

Answer 14

Branching decreases bp bc less surface area

Question 15

Does cymmetry increase or decrease mp?

Answer 15

Symmetry increases mp

Question 16

Define stereochemistry

Answer 16

The 3D structure of molecules

Question 17

Where does rotation occur in organic molecules?

Answer 17

Around c-c sigma bonds

Question 18

Define conformations

Answer 18

Different arrangements of atoms that are involved by rotation about single bonds

Question 19

What are the two types of conformations?

Answer 19

Eclipsed and staggered conformations

Question 20

Define eclipsed conformations

Answer 20

C-H bond on one carbon is directly aligned with the C-H bond of the adjacent carbon

Question 21

Define staggered conformations

Answer 21

The C-H bond of one carbon bisects the H-C-H bond angle on the adjacent carbon

Question 22

Define dihedral angle

Answer 22

The angle that separates a bond on one atom from a bond on an adjacent atom

Question 23

Does a stable molecule have higher or lower energy?

Answer 23

Lower energy, it’s not excited

Question 24

Are staggered or eclipsed conformations more stable?

Answer 24

Staggered conformations are more stable (lower in energy)

Question 25

Define torsional energy

Answer 25

The difference between staggered and eclipsed conformations

Question 26

Define torsional strain

Answer 26

An increase in the energy caused by eclipsing interactions

Question 27

Define anti rotations

Answer 27

Staggered conformation with two larger groups 180 degrees from each other

Question 28

Define gauche rotations

Answer 28

Staggered conformation with two larger groups 60 degrees from each other

Question 29

Define steric strain

Answer 29

An increase in energy resulting when atoms are forced too close to one another

Question 30

Are gauche or anti conformations more stable?

Answer 30

Anti conformations are more stable (lower in energy) bc less steric strain

Question 31

Define angle strain

Answer 31

An increase in energy when tetrahedral bond angles deviate from the optimum angle of 109.5 degrees

Question 32

What is the most common ring size in naturally occurring compounds?

Answer 32

Cyclohexanes

- 6 carbons

Question 33

What is the most stable form of a cyclohexane?

Answer 33

The chair form

• all C-C bonds are 109.5 (ideal)
• H’s are staggered and not eclipsed

Question 34

What is the structure of a cyclohexane?

Answer 34

• 3 up carbons and 3 down carbons
• axial H’s (go up and down)
• equatorial H’s (located in the plane of the ring)

Question 35

What is a conformation of the chair cyclohexane?

Answer 35

The boat cyclohexane

• the down carbon on the end flips up

Question 36

How many chair conformations of cyclohexanes exist?

Answer 36

2 with same stability

• up carbons -> down
• axial H’s -> equatorial

Question 37

Are chair or boat cyclohexanes more stable?

Answer 37

Chair bc more staggered and less torsional strain

Question 38

Is there more room for large groups on axial or equatorial positions?

Answer 38

Equatorial bs less steric interactions

Question 39

Define stereoisomers

Answer 39

Isomers that differ only in the way the atoms are oriented in space

Question 40

What are the two types of stereoisomers?

Answer 40

Cis - two groups on same side of ring

trans - two groups on opposite sides of the ring

Question 41

In monosubstituted cyclohexanes, is axial or equatorial more favored?

Answer 41

Equatorial

Question 42

In 1,2-disubstituted cyclohexanes is cis or trans more stable?

Answer 42

Trans bc 2 equatorial sites

Question 43

In 1,3-disubstituted cyclohexanes is cis or trans more stable?

Answer 43

Cis bc 2 equatorial sites

Question 44

In 1,4-disubstituted cyclohexanes is cis or trans more stable?

Answer 44

Trans bc 2 equatorial sites