Molecular Conformations: Alkanes And Cycloalkanes

Question 1

What are ISOMERS?

Answer 1

Different structures of the SAME molecular formula

Question 2

What are CONSTITUTIONAL (structural isomers)?

Answer 2

Compounds that have the same molecular formula but different atom connectivity/bonding sequence

This forms different compounds which have different physical and chemical properties (ex. BP and MP)

Question 3

What is the general formula for alkanes?

Answer 3

C(n)H(2n+2)

carbon hydrogen molecules that have sigma bonds

Question 4

How can you determine whether compounds are the same or if they are constitutional isomers?

Answer 4

1. Identify if they have the same molecular formula (if yes…)
2. Find longest c-chain (if not the same number = constitutional isomer)
3. If not, are the substituents the same and in the same position? (Yes = same compound)

Question 5

What are primary, secondary, tertiary, and quaternary carbons?

Answer 5

Primary = attached to 1 group
Secondary = attached to 2 groups
Tertiary = attached to 3 groups
Quaternary = attached to 4 groups

Question 6

Ways to represent 3D shape of a compound?

Answer 6

1. Wedge and dash
2. Sawhorse
3. Newman projection
4. Fischer projection

Question 7

What are Newman projections? What are they used for?

Answer 7

Compound representation where you are looking down a C-C bond

Useful to compare the relative stability of possible conformations resulting from single bond rotation

Question 8

What is staggered conformation? What is eclipsed conformation?

Answer 8

Staggered: bonds on adjacent carbons are as far apart as possible

Eclipsed: bonds of adjacent carbons are parallel

Question 9

What is a conformation?

Answer 9

Different spatial arrangements on atoms or groups caused by FREE ROTATION of a single bond (for alkanes, this is along the C-C bond)

Question 10

What is the dihedral/torsional angle?

Answer 10

Angle between atoms that are attached to adjacent carbons (60º)