Organic Chemistry : Help with Electron Pushing

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Electron Pushing

2-butene reacts with  (dibromine in a tetrachloromethane solvent). What is the final product?

Possible Answers:

No reaction

Correct answer:

Explanation:

Img 0636

Here we have a classic electrophilic addition reaction.

We must remember that a double bond is an area in a molecule that has a high electron density. As a result, double bonds can act as nucleophiles and react with good electrophiles.

In this problem, the alkene attacks the dibromide to form a bromonium ion, which is rather unstable. The bromonium ion pulls carbon's electrons toward itself, causing the carbons in the bromonium complex to have a slightly negative charge. As a result, the negatively charged bromine can attack either of the carbon atoms and, thus, we have added two bromines to our carbon chain.

Example Question #2 : Help With Electron Pushing

How many stable resonance structures are there for the following molecule (include the given structure in your total count)?

Screen shot 2015 10 24 at 10.14.54 am

Possible Answers:

1

6

4

3

5

Correct answer:

5

Explanation:

The five resonance structures of the given molecule are shown below:

Screen shot 2015 10 24 at 10.15.07 am

Example Question #3 : Help With Electron Pushing

Rank the following compounds in order of increasing rate of electrophilic aromatic substitution.

Screen shot 2015 09 21 at 3.10.50 pm

Possible Answers:

V, II, I, III, IV

II, I, III, IV, V

II, IV, III, I, V

IV, V, I, III, II

V, I, III, IV, II

Correct answer:

V, I, III, IV, II

Explanation:

The nitro substituent is strongly deactivating, ketones are moderately deactivating substituent, halides are weakly deactivating, alkyl groups are weakly activating, and amine groups are strongly activating.

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