Choose the correct mechanistic pathway for each of the following questions:

Chemistry

1 answer:

Evgesh-ka [11]3 years ago

8 0

Answer:

Chlorination of a 1° alcohol using Thionyl Chloride - an SN2 process

Alkene formation via POCl3 reaction with a 2º alcohol - an El process

Explanation:

For a primary alcohol, the chlorination occurs by SN2 mechanism. Remember that the order of SN2 mechanism is methyl > primary > secondary > tertiary. This means that a primary alkyl halide will undergo nucleophillic substitution by SN2 mechanism.

For a secondary alkyl halide, we normally expect that the mechanism will be E2. When we use POCl3 and pyridine, the alkyl halide passes through a carbocation intermediate which is characteristic of an E1 mechanism.

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What is the entropy of this collection of training examples with respect to the positive class B. What are the information gains

Alenkinab [10]

The data set is missing in the question. The data set is given in the attachment.

Solution :

a). In the table, there are four positive examples and give number of negative examples.

Therefore,

$P(+) = \frac{4}{9}$ and

$P(-) = \frac{5}{9}$

The entropy of the training examples is given by :

$-\frac{4}{9}\log_2\left(\frac{4}{9}\right)-\frac{5}{9}\log_2\left(\frac{5}{9}\right)$

= 0.9911

b). For the attribute all the associating increments and the probability are :

$a_1$ + -

T 3 1

F 1 4

Th entropy for $a_1$ is given by :

$\frac{4}{9}[ -\frac{3}{4}\log\left(\frac{3}{4}\right)-\frac{1}{4}\log\left(\frac{1}{4}\right)]+\frac{5}{9}[ -\frac{1}{5}\log\left(\frac{1}{5}\right)-\frac{4}{5}\log\left(\frac{4}{5}\right)]$

= 0.7616

Therefore, the information gain for $a_1$ is

0.9911 - 0.7616 = 0.2294

Similarly for the attribute $a_2$ the associating counts and the probabilities are :

$a_2$ + -

T 2 3

F 2 2

Th entropy for $a_2$ is given by :

$\frac{5}{9}[ -\frac{2}{5}\log\left(\frac{2}{5}\right)-\frac{3}{5}\log\left(\frac{3}{5}\right)]+\frac{4}{9}[ -\frac{2}{4}\log\left(\frac{2}{4}\right)-\frac{2}{4}\log\left(\frac{2}{4}\right)]$