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

#Chemistry

Easy Math Editor

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.
Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

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

Math	Appears 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}`	$\boxed{123}$

Comments

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

Ameya Daigavane - 5 years 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

AYUSH JAIN - 5 years 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.

Ameya Daigavane - 5 years ago

@Ameya Daigavane – thank you sir for your kind reply.

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.

AYUSH JAIN - 5 years ago

@Ayush Jain – 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.

Ameya Daigavane - 5 years ago

@Ameya Daigavane – 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 .

AYUSH JAIN - 5 years ago

@Ayush Jain – 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.

Ameya Daigavane - 5 years ago

Math	Appears 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}`	$\boxed{123}$