OChem Ch 3 Structure and Stereochemistry of Alkanes
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common alkane names
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
- CH3 CH3 C2H5
- | | |
when looking for the longest chain, what if there are two possible chains with same number of carbons
use the chain that has the most substituents
when numbering the carbons, what if you have two substituents that are equidistant?
look for the next closest group.
The carbon on the left is labeled 1 because it has a substituent next to it
what does it mean if an alkyl group has an "n-" prefix
n- stands for normal. It means that the alkyl group is bonded to the main carbon chain via its terminal carbon.
name all butyl groups
what is a primary/secondary/etc. carbon?
primary- bonded to one other carbon
secondary - bonded to two other carbons,
how to name complex substituents?
- •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
if you increase branching in alkanes, the b.p. will ______ and the mp will _______
major reaction done by orgo chemists with alkanes?
- 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
what is the conformation of higher alkanes (nonane, decane, etc.)
- •Anti conformation is lowest in energy.
- •“Straight chain” actually is zigzag.
- 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:
- half chair
what is a bicyclic alkane
two alkane rings bonded together
fused rings and bridged rings
fused rings share two adjacent carbons
bridged rings share two nonadjacent C's
name the following bridged ring:
name the following fused ring:
which is more stable cis or trans decalin?
trans, b/c there is torsional strain in cis:
What is the torsional strain here called?
What is the most stable conformation of trans 1-ethyl-3-methylcyclohexane?
for cis bonds in cyclohexane, what is the spatial positioning of the cis bonds (think in terms of equatorial and axial)
one equatorial, one axial
How does the conformer of cyclohexane change when it has bulky functional groups?
- •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.
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