OChem Ch 3 Structure and Stereochemistry of Alkanes

methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane

• 1. find longest continuous carbon chain
• 2. number the carbons, starting closest to the first branch
• 3. name the groups attached to the chain using the carbon number as their locator
• 4. alphabetize substituents (ignoring the di- tri-, etc. and just focusing on the name of the substituent group, like methyl, ethyl, etc.)
• 5. use di- tri-, etc. for multiples of same constituent

• ex. 
•           CH3 CH3 C2H5
•              |         |         | 
• CH3---CH--CH--CH--CH3

name: 2,3-methyl-3-ethylpentane

use the chain that has the most substituents

look for the next closest group.

ex.



The carbon on the left is labeled 1 because it has a substituent next to it

n- stands for normal. It means that the alkyl group is bonded to the main carbon chain via its terminal carbon.

ex.

• n-propyl:
• CH3CH2CH2-

• n-propyl:
• CH3CH2CH2-

• isopropyl:
• CH3--CH--CH3
•           |

n-butyl:

CH3CH2CH2CH2-

sec-butyL-

• CH3--CH--CH2--CH3
•             |

• isobutyl
•          CH3
•               |
• CH3---CH---CH2-

TERT-BUTYL

•        CH3
•             |
• CH3---C--CH3
•             |

primary- bonded to one other carbon

secondary - bonded to two other carbons,

etc.

• •If the branch has a branch, number the carbons from the point of attachment.
• •Name the branch off the branch using a locator number.Parentheses are used around the complex branch name

ex.

decrease, increase

halogenation

• CH4 +Cl2 --> CH3Cl + CH2Cl2 + CHCl3 + 
•                    ^                                  CCl4                                
•                     |
•           add heat or light
•                

structure resulting from the free rotation of a C--C single bond.

• 1. Staggered
• -dihedral angle -- 60 degrees
• lower in energy-- stable

• 2. eclipsed
• 0 degrees- dihedral angle
• least stable-- high energy

• 
• 3. skew
• -anything between eclipsed and staggered

• 1. totally eclipsed
• least stable
• dihedral angle 0 degrees

• 
• 2. anti conformer
• lowerst energy
• dihedral angle - 180 degrees
• 

• 3. eclipsed
• 2nd highest in energy (2nd most unstable)
• dihedral angle 120 degrees
• 

• 4. gauche, staggered conformer
• dihedral angle - 60 degrees
• 2nd most stable
• 

• •Anti conformation is lowest in energy.
• •“Straight chain” actually is zigzag.

• formula:CnH2n
• mp and bp similar to branched alkanes with same number of carbons

1. number carbons in ring if >1 substituent. First in alphabet gets lowest number,

2. proceed in naming the same way you would any other hydrocarbon

5 and 6 member rings the most stable b/c bond angles closest to 109.5 degrees. All other rings exhibit angle strain.

• large ring strain due to angle compression. Very reactive, weak bonds. Torsional strain because of elclipsed hydrogens.
• 

angle strain due to compression. Torsional strain partially relieved by ring-puckering (see the bent shape of the newman projection to get an idea of what puckering looks like)

puckered conformer reduces torsional strain

• From most stable to least stable:
• chair
• twist
• boat 
• half chair

two alkane rings bonded together

fused rings share two adjacent carbons

bridged rings share two nonadjacent C's

bicyclo[3.2.1]octane

bicyclo[4.2.0]octane

trans, b/c there is torsional strain in cis:

1,3-diaxial interactions

one equatorial, one axial

• •Groups like t-butyl cause a large
• energy difference between the axial and equatorial conformer. 

•Most stable conformer puts t-butyl equatorial regardless of other substituents.