# organic chemistry

In aldol reaction we use a base such as NaOH Which takes away alpha hydrogen of aldehyde or ketone.

Will grignard reagent do aldol reaction or addition reaction in ketone or substitution of Br in the reactant shown below. Taking only one mole of grignard reagent and if needed water can be added.

BrCH2CH2CH2COCH3

Note by Ayush Jain
3 years, 4 months ago

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

• Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
• Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
• Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold
- bulleted- list
• bulleted
• list
1. numbered2. list
1. numbered
2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in $$ ... $$ or $ ... $ to ensure proper formatting.
2 \times 3 $2 \times 3$
2^{34} $2^{34}$
a_{i-1} $a_{i-1}$
\frac{2}{3} $\frac{2}{3}$
\sqrt{2} $\sqrt{2}$
\sum_{i=1}^3 $\sum_{i=1}^3$
\sin \theta $\sin \theta$
\boxed{123} $\boxed{123}$

Sort by:

Grignard reagent will add to the ketone, in a nucleophilic addition at the carbonyl group.

- 3 years, 4 months ago

Actually answer is it will add to ketone and then negative charge on O will substitute br to form 5 membered ring.

I wanted to know the reason why grignard reagent being a strong base cannot take away alpha hydrogen of ketone and form 5membered ring substituting Br to form cyclopentanone

- 3 years, 4 months ago

Yep, that is correct. Grignard reagents selectively attack carbonyl groups. Only if the group is sterically hindered, will it act as a base, taking the alpha hydrogen.

There are two points to be considered here:

Grignard reagents are better nucleophiles than bases.

The alpha hydrogen is much less acidic (about 10^-15 times the pKa) than a carboxylic acid group. Even though there are many reactions that involve alpha hydrogen abstraction, it really isn't very acidic by any means.

- 3 years, 4 months ago

sir please tell me why OH is not a good nucleophile while Grignard reagent is.

Also sir if in a compound in which like HCCCHO ie combination of alkyne and aldehyde, how will NaOH and Grignard reagent react separately . Do they react in same manner or different.

- 3 years, 4 months ago

OH is a worse nucleophile than a base, because of H-bonding. This is similar to reason why F- is the weakest nucleophile in protic solvents, but the strongest in aprotic.

I would recommend you to remember the trends, as the reasoning can really go either ways.

NaOH is not strong enough to abstract terminal alkyne hydrogens, but Grignard reagents can and will. I do not think the Grignard reaction will proceed here.

- 3 years, 4 months ago

But I have read in Solomons and fryhle that alpha carbon is more acidic than terminal hydrogen of alkyne . So should extract alpha hydrogen . Please reply .

- 3 years, 4 months ago

See here and here (under acidity of terminal alkynes).

You make a fair point. Perhaps the presence of Li+ cation stabilises the intermediate in the alkyne + Grignard reaction.

- 3 years, 4 months ago