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Santa Barbara City College

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Exam 1 answers

Q1. Monochlorination can occur in as many as non-equivalent positions there are in

ethylcyclohexane. The six positions that can be chlorinated are shown below

Thus, there can be as many as six monochlorination products at any of this positions.

Q3. In this case, it’s always useful to identify the monomer within the polymer chain. The

monomer is the single unit that repeats over and over within the chain. It is highlighted in red in

the structure below.

Thus, considering the electronic movement, the structure that resembles the most this monomer

is B. It is not D because the linkage between aromatic rings would contain 4 carbons instead of 2.

Q4. Indeed the product shown is one of the product due to the formation of a free radical in that

position. However, free radicals have resonance structures. One of these resonance structures

leads to a free radical in the terminal carbon, and thus, two products are formed. The two free

radicals are shown below

Each one of them leads to a different bromination product.

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Q5.

The dissociation energy for F-F bond is 155 kJ/mol. It might seem high, but the main problem is

to control the chain reaction started by fluorine free radical. Given its small size it’s extremely

reactive and can initiate a great number of propagations steps making it difficult to form specific

products.

On the other hand, bond dissociation energy for I-I is about 152.5 kJ/mol. However, even when

it’s about the same energy, iodine is a bigger atom capable of stabilizing the recently formed free

radical and thus, poorly reactive in the propagation step making it useless in these reactions.

Q6. This is a hydrobromination reaction promote by peroxides, which induces the addition to occur

via free radical. Thus, the addition of bromine occurs in the less substituted carbon of the double

bond, instead of the typical product (which would be the selected answer B). The correct answer

is C. Neither A nor D are formed, since no free radicals are formed, or could have resonance

structures, in this positions.

Q7. With respect to the resonance theory, in the case of 3-chloroprop-1-ene an allylic carbocation

is formed, which is stabilized by resonance making it far more stable than in the case of 1-

chloropropane in which a primary carbocation is formed.

As for the Hammond postulate, given that the carbocation formed by the alkene is more stable,

and therefore lower in energy, it resembles the most the structure of the starting material and the

energy needed for the reaction to complete is considerably lower than in the case of 1-

chloropropane.

Q11. The kinetic product is the one that forms the fastest but it’s less stable when compared to the

thermodynamic product. In the case of alkenes, the kinetic product is associated with the less

substituted alkene, which is structure B. Structure A is the thermodynamic product.

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Exam 1 answers Q1. Monochlorination can occur in as many as non-equivalent positions there are in ethylcyclohexane. The six positions that can be chlorinated are shown below 2 4 5 6 3 1 4 5 Thus, there can be as many as six monochlorination products at any of this positions. Q3. In this case, it’s always useful to identify the monomer within the polymer chain. The monomer is the single unit that repeats over and over within the chain. It is highlighted in red in the structure below. Thus, considering the electronic movement, the structure that resembles the most this monomer is B. It is not D because the linkage between aromatic rings would contain 4 carbons instead of 2. Q4. Indeed the product shown is one of the product due to the formation of a free radical in that position. However, free radicals have resonance structures. One of these resonance structures leads to a free radical in the terminal carbon, and thus, two products are formed. The two free radicals are shown below Each one of them leads to a different bromination product. Q5. The dissociation energy for F-F bond is 155 kJ/mol. It might seem high, but the main problem is to control the chain reaction started by fluorine free radical. Given its small size it’s extremely reactive and can initiate a great number of propagations steps making it difficult to form specific products. On the other hand, bond dissociation energy for I-I is about 152.5 kJ/mol. However, even when it’s about the same ener ...
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Tags: Chemistry questions ethylcyclohexane aromatic rings monochlorination products Electronic Movement