Organic Chemistry Laboratory I - Chem 341

Quiz 1a

1. Draw the Newman projection of the staggard conformation (rotomer) for n-butane looking down the C2-C3 bonds. (2 pts)

The highest energy rotomer has the methyl groups eclipsed with each other and the lowest energy conformation is in the staggered when the methyls are on opposite sides from each other.

2. What is the IUPAC name for the following compound? (2 pts)

1-bromobutane, 1pt for bromo or butane

3. When is it appropriate to use a “mixed solvent” recrystallization? (2 pts)

A mixed solvent recrystallization is used when the compound is too soluble in most common solvents and we cannot find a single solvent where it is only soluble at elevated temperature. In this case we use a solvent where it is very soluble (e.g. methanol) and then add a second solvent that it is not soluble in (e.g. water). Thus, the mixture of the two solvents makes the compound soluble at elevated temperatures, but not at room temperature.

4. Consider the following compound and answer the questions below.

(a) Draw the lowest energy chair conformation. (1 pt)

A and B are equal in energy since there is always one chlorine atom in the axial and equatorial position for the trans compound.

(b) How many equatorial chlorine atoms are in the highest energy conformation? (1 pt)

One chlorine is always in the equatorial position for this trans compound

5. Why is flameless heating used in a recrystallization when hexane or diethyl ether is used as the solvent? (1 pt)

Flameless heating is used because most organic solvents are flammable, especially diethyl ether, which has a very low flash point (-40 ^oC).

6. Does a pure compound have a higher or lower melting point than an impure compound? (1 pt)

The purity of our compounds in this experiment were assessed by melting point. A pure compound will have a well-defined melting point range, which is higher and narrower than that of an impure compound. The m.p. should be as close as possible to the literature value.