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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: theanonymous on October 09, 2012, 05:53:42 PM

Title: Write a reaction, draw potential energy diagram, explain rate of reaction?
Post by: theanonymous on October 09, 2012, 05:53:42 PM
Here is the question and how I tried to solve it...Can you please tell me if I'm right? If not, can you show me what the answer should be?

1. tert-Butyl alcohol is converted to tert-butyl bromide upon treatment with aqueous HBr at room temperature. The rate law for this reaction is unimolecular: the rate of product appearance is proportional to [t-BuOH] and independent of [HBr].

A. Please draw a detailed, arrow-pushing mechanism for this reaction.

(CH3)3COH + HBr :rarrow: (CH3)3CBr + H2O

IMAGE: http://www.imagebam.com/image/34f16e214348552

Does that look right?

B. Please draw a potential energy diagram for this reaction, using Erelative as the vertical axis and the 'reaction coordinate' as the horizontal axis.

IMAGE: http://www.imagebam.com/image/40eb85214350621

Does that look right?

C. Please briefly explain why the rate of the reaction does not depend on [HBr].

Because it depends only on the concentration of alcohol (?)
Title: Anyone really good at Organic Chemistry I? I need help. Is this right?
Post by: theanonymous on October 09, 2012, 06:26:07 PM
2. n-Butyl alcohol is converted to n-butyl bromide apon treatment with aqueous HBr at 120°C. The rate law for this reaction is bimolecular: the rate of product appearance is proportional to both [n-BuOH] and [HBr]

A. Please draw a detailed arrow-pushing mechanism for this reaction.

Is it this?

CH3CH2CH2CH2-OH  :rarrow: CH3CH2CH2CH2-Br + H2O

IMAGE: http://www.imagebam.com/image/53678f214354002

B. Please draw a potential energy diagram for this reaction, using Erelative as the vertical axis and the 'reaction coordinate' as the horizontal axis.

IMAGE: http://www.imagebam.com/image/cb5e57214353624

Does that look right?

C. Please briefly explain why the rate of the reaction depends on [n-BuOH] and [HBr].

Help???
Title: Re: Anyone really good at Organic Chemistry I? I need help. Is this right?
Post by: Dan on October 09, 2012, 06:34:11 PM
Quote from: theanonymous on October 09, 2012, 06:26:07 PM
2. n-Butyl alcohol is converted to n-butyl bromide apon treatment with aqueous HBr at 120°C. The rate law for this reaction is bimolecular: the rate of product appearance is proportional to both [n-BuOH] and [HBr]

A. Please draw a detailed arrow-pushing mechanism for this reaction.

Is it this?

CH3CH2CH2CH2-OH  :rarrow: CH3CH2CH2CH2-Br + H2O


No, "arrow-pushing mechanism" means you need to use curly arrows to show how the reaction happens. What you have done is show the starting materials and the products with no indication of how the reaction happens - e.g. SN1, SN2 etc.. Look up "mechanism" in any organic textbook. There will be a chapter on (aliphatic) nucleophilic substitution that you need to read.
Title: Re: Write a reaction, draw potential energy diagram, explain rate of reaction?
Post by: discodermolide on October 10, 2012, 12:04:09 AM
In your mechanism you do not show any arrows as requested. The arrows are used to show your understanding of what is going on in the conversion, indicating the movement of electrons in going from the SM to product. Look at any textbook on mechanisms in organic chemistry, for example "A guidebook to mechanism in organic chemistry; sixth edition" by Sykes,P.. Amazon has it. I think I have the first or second edition. Great book.