McMurry (Kap.4,3)

Question 1

Adolf von Bayer introduced the term “angle strain”. What does it mean?

Answer 1

He suggested that some rings might be unstable due to angle strain, which is caused when the bond angles in a molecule are forced to deviate from the ideal 109grader tetrahedral value.

Question 2

By an experiment run on page 94 to find out about the cycloalkane strain energies, what is the results?

Answer 2

By calculating the difference between cycloalkane heat of combustion and the open chain alkane heat of combustion, the difference in heat let out tells about the strain (more heat - more strain/energy).

It was found that small and medium rings were strained, BUT cyclohexane and very large rings were strain free.

Question 3

Bayer assumed that cyclohexane should be the most strained cyclohexane out of all of them. Why was he wrong?

Answer 3

Because he thought of the rings as being flat, but actually they adopt a puckered 3d conformation that allows bond angles to near the ideal 109 grader, therefore reducing the strain. Therefore, strain occurs only in small rings with less flexibility.

Question 4

Would you expect a bigger ring or a smaller ring to have more strain?

Answer 4

The smaller ring because strain occurs particularly in small rings with less flexibility.

Question 5

Three kinds of strain contribute to the energy of cycloalkanes. What are they?

Answer 5

1) Angle strain (when the angles are way off 109 grader)

2) Torsional strain (when the compound is in eclipsed form, and for example the H-H is close together).

3) Steric strain (when repulsion between atoms occur, because they are too close together).