I am very confused on a few things regarding chair conformation (mainly in regards to hoe axial vs. equatorial positioning affects the structure). I guess what I am looking for is a general tutorial of how quite a few things work.
I have encountered quite a few questions on homework assignments that require knowledge of the following:
1) Knowing what the highest and lowest chair conformations would be when creating a chair conformation structure from a lewis structure/equation (most problems have a combination of many different side groups, like trans-1-bromo-2-isopropylcyclohexane)
2) Finding the lowest/highest energy structure while keeping stereochemistry R or S in mind (like (2R,3R)-2-bromo-3-phenylpentane)
3) Determining whether a substituent is in equatorial or axial position when the structure is NOT in the chair conformation (see attachment)
4) Lastly, in reactions like (E2) elimination, how do I know which carbon to form the double bond between when the carbon attached to the leaving group is attacked to more than one other carbon. I know this has something to do with the positioning, but am not sure why.
I know it is a lot of question, but this is a huge component of my upcoming organic chemistry exam. I understand most of it, but this plays such an important role in my ability to answer the questions correctly and efficiently.
I have attached two practice problems (as noted in #3) and was wondering if these could be used as an example of how to do what I asked in #3.
This solution assists with the chair conformation problem.
5 Chemistry Problems on alkanes
1. Which of the following correctly lists the following isomeric alkanes in order of increasing boiling point? n-hexane, 2,3-dimethylbutane, 2-methylpentane
a. n-hexane < 2-methylpentane < 2,3- dimethylbutane
b. 2-methylpentane < 2,3-dimethylbutane < n-hexane
c. 2,3-dimethylbutane < 2-methylpentane < n-hexane
d. n-hexane < 2,3-dimethylbutane < 2-methylpentane
2. Which of the following statements about n-heptane is true?
a. It is non-polar and water soluble
b. It is polar and water soluble
c. It is polar and water insoluble
d. It is non-polar and water insoluble
3. The number of constitutional isomers that are alkanes that can be drawn for C4H8 is
4. Which compound would be expected to show the most strain per -CH2- ?
5. Which of the statements below correctly describes the chair conformations of trans-1,2-dimethylcylcohexane?
a. The two chair conformations are identical in energy
b. The higher energy conformation contains one axial methyl and one equatorial methyl group
c. The lower energy conformation contains two axial methyl groups
d. The lower energy conformation contains two equatorial methyl groups.