Part 1

Question 8

Alkynes

Answer 8

Cn H2n-2 (triple bond)

Physical properties are similar to alkenes and alkanes.

Shorter = gases, boiling at high T than alkenes.

Question 9

Nomenclature

Answer 9

1. Multiple bonds should be on backbone.
2. -OH is high priority (placed above multiple bond)
3. Haloalkanes, ethers, and ketones are often given common names (e.g. methyl chloride, diethyl ketone)
4. Aldehydes/carboxylic acids are terminal functional groups
5. Specify isomer, if relevant (such as cis/trans, R or S, etc).

Question 10

Isomers

Answer 10

Chemical compounds that have same molecular formula, but differ in structure.

May be extremely similar or extremely different.

Question 11

Structural Isomers

Answer 11

Share only their molecular formula, but their atomic connectivity is different.

Therefore, they may have very different chemical and physical properties.

Question 12

Stereoisomers

Answer 12

Have same atomic connections, but the atoms are arranged differently in space.

Examples:
Geometric isomers, Enantiomers, Diastereomers, Meso Compounds, and Conformational.

Question 13

Chirality

Answer 13

Carbon atoms have four different substituents.

Question 14

Geometric Isomers

Answer 14

Differ in position of substituents attached to a double bond.

Cis (Z) - Substituents on same side (based on high atomic number)

Trans (E) - Substituents are on opposite sides.

Question 15

Enantiomers

Answer 15

Chiral objects that are non-superimposable mirror images.

Specific type of stereoisomers.

Question 16

Absolute Configuration

Answer 16

(R) and (S) notation.

• Think of a steering wheel.
• Lowest priority substituent is in fourth position and should point away from you, down the column.
• While #1, 2, and 3 lie on the wheel itself.
• R is clockwise, and S is counterclockwise.

Question 17

Fischer Projection

Answer 17

Horizontal lines indicate bonds that project from plane of page, while vertical lines behind plane of page.

Question 18

Racemic mixture

Answer 18

Mixture of equal concentrations of both the (+) and (-) enantiomers.

Rotations cancel each other out, thus NO optical activity.

Question 19

Diastereomers

Answer 19

Differ in chirality, but are NOT mirror images.

For any molecule with n chiral centers, there are 2^n possible stereoisomers.

e.g. Compound with 2 chiral centers = 4 stereoisomers.

Question 20

Meso Compounds

Answer 20

Have a mirror image that is superimposable.

Thus, NOT optically active.

Have a mirror plane of symmetry

Question 21

Conformational Isomers

Answer 21

Differ only by rotation about one or more single bonds.

Analogous to a person sitting or standing.

Can be seen in Newman projection.

Question 22

Newman Projection

Answer 22

Line of sight extends along a carbon carbon bond axis. (Gauge, anti, eclipsed versions)

Question 23

Straight-Chain Conformations

Answer 23

gauche < eclipsed < totally eclipsed

anti isomers have lowest energy
totally eclipsed have highest energy

At RT these easily interconvert

Question 24

Cyclic Conformations

Answer 24

Strain Energy is due to ring strain, angle strain, torsional strain, and nonbonded strain (van der waals)

Chair and boat conformations are most important forms of cyclohexane. Chair is most stable and lowest energy.

Question 25

Axial Substituents

Answer 25

Axial substituents are on Vertical Axis, like axial skeleton.

Axial is NOT favored.

Question 26

Equatorial Substituents

Answer 26

Equatorial substituents go around the middle, like earth’s equator.

Equatorial is favored over axial.

A bulky substituent can prevent the ring from adapting certain conformations.

Question 27

Hybridization

Answer 27

Concept of mixing atomic orbitals to form new hybrid orbitals.

Useful in explanation of shape of molecular orbitals.

Question 28

Bonding Summary (single, double, and triple bonds)

Answer 28

Single bonds: sigma, sp^3, 109.5 degrees

Double bonds: sigma/pi, sp^2, 120 degrees

Triple bonds: sigma/pi/pi, sp, 180 degrees

Question 29

Free Radical Halogenation

Answer 29

One or more H atoms are replaced by halogen atoms (Cl, Br, or I) via free radical substitution. Occurs in Alkanes.

Three steps:

1. Initiation
2. Propagation
3. Termination

Bromine is slow and picky and attacks most substituted.
Chlorine is rapid and attacks primary H with abundance.

Question 30

Combustion

Answer 30

Occurs in Alkanes.

Reaction of alkanes with molecular oxygen.

Forms CO2, Water, and Heat (desired product)

Question 31

Pyrolysis

Answer 31

Occurs in Alkanes.

Also called cracking”.