W19 Alkanes, Cycloalkanes and Alkyl Halides

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons containing only H and sp3 hybridised carbons

Question 2

What are the 2 types of alkanes?
General formula?

Answer 2

1. n-alkanes (“normal” alkanes): chains of -CH2- groups (methylene groups), terminated at each end by a hydrogen atom and not branched
2. Branched alkanes: structural isomers of n-alkanes
3. CnH(2n+2)

Question 3

Are alkanes polar?

Answer 3

No, they are Non-polar molecules: dissolve in non-polar or weakly polar organic solvents and are hydrophobic
Less dense than water and insoluble in water

Question 4

Rotation occurs in..
What are each structure generated by the rotation called?

Answer 4

Single bonds, but not in double bonds
Conformer or Conformational isomer

Question 5

What is meant by lowest-energy conformation?

Answer 5

The one with minimal electrostatic repulsion between bonds

Question 6

Conformational Equilibria-Ethane:
What is plotted on this graph?

Answer 6

We can plot energy against dihedral angle (H-C-C-H)

Question 7

What are cycloalkanes and their general formula?

Answer 7

Alkanes that contain rings of carbon atoms
Simple cycloalkanes are rings of -CH2- groups
CnH2n

Question 8

Isomerism in cycloalkanes
A cycloalkane has….faces
What are they called?

Answer 8

Two distinct faces
Two substituents point toward the same face: cis
Two substituents point toward opposite face: trans

Question 9

Cycloalkanes may experience angle strain and torsional strain = ring strain - why?

Answer 9

Their bond angle is smaller/reduced inside of the ring ( <109.5°)
Strain can be reduced by deviating from a planar structure

Question 10

What are Nucleophiles?
Examples

Answer 10

-They “Love nuclei”.
-Wish to form bonds by donating or sharing their electrons
Nucleophiles are electron rich and can be negative ions, or neutral molecules with electron lone pairs
e.g. OH- H2O R-OH R-NH2

Question 11

What are Electrophiles?
Examples?

Answer 11

-They “love electrons”
-Wish to form bonds by accepting electrons or sharing electrons with a reactant molecule.
-Electrophiles are electron deficient and can be positive ions or neutral (but δ+) molecules
e.g. A haloalkane

Question 12

Staggered conformation
Eclipsed conformation

Answer 12

=Low energy conformation
=High energy

Question 13

Gauche conformation?

Answer 13

All the bonds are staggered, but the big substituents, so the two methyl groups are still near one another

Question 14

Benzene vs Cyclohexane

Answer 14

Cyclohexane is NOT flat but benzene is

Question 15

Chair conformation
ADEU acronym?

Answer 15

Axial substituents: drawn vertically (1 each C)
Equatorial substituents: drawn parallel (1 each
C) to the next-but-one C-C bond

Axial Down, Equatorial Up