[Rutherford]

1.Does this alcohol http://imageshack.us/photo/my-images/41/48178882.gif/ give only one alkane as a product after dehidratation with H₂SO₄ and reaction with HCl? I think there should be two, one is the mayor product according to Markovnikof's rule.

2.How many fractions that were obtained from the fraction destillation of 3-methyl-2-penthanole are optical active? The answer is none, why?

[discodermolide]

1.Does this alcohol http://imageshack.us/photo/my-images/41/48178882.gif/ give only one alkane as a product after dehidratation with H₂SO₄ and reaction with HCl? I think there should be two, one is the mayor product according to Markovnikof's rule.

2.How many fractions that were obtained from the fraction destillation of 3-methyl-2-penthanole are optical active? The answer is none, why?

question 2: you cannot separate enantiomers by distillation.

question 1: I think you will get 1 product.

[Rutherford]

In the answer it says: there are 2 different fractions, none is optical active. What are those 2 fractions?
Can you draw the product?

[discodermolide]

In the answer it says: there are 2 different fractions, none is optical active. What are those 2 fractions?
Can you draw the product?

I assume you mean 3-methyl-pentan-2-ol?
2 chiral centers = 4diastereoisomers, (R)(R), (S)(S), (R)(S) and (S)(R). You tell me which are those that appear in the distillate.

[Rutherford]

I am not sure how to determine that.
And what is the product in question 1?

[discodermolide]

I am not sure how to determine that.
And what is the product in question 1?

Above you said "3-methyl-2-penthanole" I am asking if you meant pentanol?

What are not not sure about determining?

[Rutherford]

Yes, it is pentanol, how to determine what stereoisomers appear in the distillate and why?

[discodermolide]

Yes, it is pentanol, how to determine what stereoisomers appear in the distillate and why?

As I said you cannot separate enantiomers by distillation.
This compound has 4 diastereoisomers, (R)(R), (S)(S), (R)(S) and (S)(R).
I'm asking you, which do you think are the enantiomeric pair?

[orgopete]

These questions seem to be about diastereomers and contain some ambiguity about the specifications. For the reaction of 2,5-dimethylcyclopentanol with sulfuric and addition of HCl to the resulting alkene, I am going to presume we get a single intermediate, 3-methylcyclopentene. Addition of HCl to that will give 1-chloro-1,3-dimethylcyclopentane. However, there are now two chirality centers, neither of which should have been stereospecific, therefore a diastereomeric mixture of products result.

For question two, although it states the product is optically active, it does not preclude that it is also a diastereomeric mixture. If it were a single compound, then distillation should give a single fraction. If the answer is there are two fractions, then it is indicating the material was an optically active diastereomeric mixture of alcohols. If I were writing this question, I might ask students to explain how this optically active material could give two fractions and see if anyone could realize that the material had to have been a diastereomeric mixture.

(I prefer to embed images in the chemicalforum itself (additional options…) as I have found external hosted images sometimes disappear over time.)

[Rutherford]

Shouldn't 2-chloro-1,3-dimethylcyclopentane be made also?
The second question seems beyond general high school knowledge, so I have to study it more first.

[discodermolide]

Question 2 does not say that the products are optically active,

"2.How many fractions that were obtained from the fraction destillation of 3-methyl-2-penthanole are optical active? The answer is none, why?"

The answer is none because you cannot separate enantiomers by distillation.
Previously I gave the answer to the composition of the two fractions.
Fractional distillation of diastereoisomers, (R)(R), (S)(S), (R)(S) and (S)(R)

[orgopete]

Although 2-chloro-1,3-dimethylcyclopentane could be formed, I think your answer should be consistent with the general theme of both questions, namely diastereomers. In that case, the (1R,3S) and (1S,3R) are enantiomers of one diastereomer and the (1R,3R) and (1S,3S) would be the other, so two products.

2.How many fractions that were obtained from the fraction destillation of 3-methyl-2-penthanole are optical active? The answer is none, why?

In the answer it says: there are 2 different fractions, none is optical active. What are those 2 fractions?

Okay, I misunderstood the question, I thought the 3-methyl-2-pentanol was optically active, wrong. The answer is as disco advised.

[Rutherford]

If 2-chloro-1,3-dimethylcyclopentane could be formed, even in traces, I think that the question should be different.

3-methyl-2-pentanol is optically active with two chiral centers, I am not familiar with diastereoisomerism yet, so after I read some texts I will return to the second question later.

[Rutherford]

Back to the 2nd question:
I have 3-methyl-pentan-2-ol, which has 2 chiral centers. (R)(R), (S)(S), (R)(S) and (S)(R) are the diastereoisomers, the enantiomers are (R)(R) and (S)(S).
discodermolide, you said that enantiomers cannot be separated by destillation, but there are still 2 fractions. What is in the 1st and what in the 2nd fraction, and why? I can't figure out this.

[discodermolide]

Back to the 2nd question:
I have 3-methyl-pentan-2-ol, which has 2 chiral centers. (R)(R), (S)(S), (R)(S) and (S)(R) are the diastereoisomers, the enantiomers are (R)(R) and (S)(S).
discodermolide, you said that enantiomers cannot be separated by destillation, but there are still 2 fractions. What is in the 1st and what in the 2nd fraction, and why? I can't figure out this.

The two fractions are each of the diastereoisomeric pairs.