CH 106 - Lesson 2

Lesson 2 Review Answers

1.      Name the following molecules.

a.      3-chloro-4-methyl-1-cyclopentene

b.      3-methyl-2-pentene

c.      4,4-dimethyl-2-pentyne

d.      m-chorophenol or 1-chloro-3-hydroxybenzene

e.      poly-1-chloro-1-propene

2.      Draw the following molecules.

3.      Draw then name, the five possible non-cyclic isomers of C₅H₁₀.

4.      The below names are incorrect.  State what is wrong and give the correct name.

a.      4-(chloromethyl)-2-pentene        The methyl group and the chloro group need to separate branches when naming the compound.  It should be 4-chloro-4-methyl-2-pentene.

b.      trans-1-pentene   We have only one possible geometric isomer for 1-pentene so cis & trans do not apply.  It should be simply 1-pentene.

c.      1-chloro-2-phenol            Since we are using the base phenol, the hydroxyl group is attached to carbon #1, and the chloro group to carbon #2.  The name should be o-chlorophenol.

5.      Explain how you would differentiate between benzene and cyclohexane with IR data only.

Although both molecules contain six carbons in a ring structure, the difference is the presence of double bonds.  Cyclohexane’s IR would show only the sp³ C-H bonds to the immediate right of 3000cm^-1.  For benzene, we would see the sp² C-H bonds to the immediate left of 3000cm^-1.  The C=C double bonds in benzene would also have two peaks in the 1500-2000cm^-1 range.  These peaks would not be present in cyclohexane.

6.      For the compounds below, state the number of pi and sigma bonds present and also include the hybridization of the starred (*) carbons.

a.      σ bonds = 11, π bonds = 1, * carbon = sp²

b.      σ bonds = 12, π bonds = 3, * carbon = sp²

c.      σ bonds = 9, π bonds = 2, * carbon = sp

d.      σ bonds = 4, π bonds = 0, * carbon = sp³

7.      A compound has the following IR and when burned on a copper wire, no change was seen in the flame.  Initially, no reaction was seen with Br₂ (in 1,1,1-trichloroethane) but when a few iron fillings were added, the bromine color disappeared. What is most likely to be the class of the organic molecule?

The data indicates that the compound is aromatic.  Since it does not react in the flame test, a halide is not present and therefore not an alkyl halide.  The Br₂ reaction without Fe present shows it is not an alkene but could be an alkane, an alkyl halide (which has already been disproved) or an aromatic.  When the Fe was added, the reaction proceeded, which shows that a catalyst is needed, which shows that the compound is aromatic.  The IR also shows this with peaks to the immediate left of 3000cm^-1 and multiple peaks in the 1500-2000cm^-1 range which as all present in aromatic compounds.

8.  Predict the products for the following reactions.