Organic chemistry question. Mcat review question

In summary, the question is asking what the most likely heat of hydrogenation would be for a compound formed by dehydrating 1-butanol. The answer is between 30 and 33 kcal/mol, based on a table of heats of hydrogenation provided. While a product that is more kinetically favored may form faster, it is more likely that the product will be the one that is thermodynamically favored. In order for a reaction to be thermodynamically favored, it must be reversible. However, the question may not include the two 2-butenes listed in the table. Using strong acid and proper conditions may lead to rearrangement, but it could also cause unwanted side reactions. Typically, dehydration reactions are performed to
  • #1
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If you dehyrate 1-butanol, wouldn't you get 2-butene due to rearrangement? This is not a homework question. This is an mcat review question. The question asks: when 1-butanol is dehydrated, the new compound's heat of hydrogenation is most likely? The answer is between 30 and 33 kcal/mol

It gives you a table of heats of hydrogenation
1-butene 30.3
1-pentene 30.1
cis-2-butene 28.6
trans-2-butene 27.6

I'd assume that the new compound would have a heat of hydrogenation similar to trans-2-butene since the carbocation would undergo rearrangement. It is more thermodynamically favored. However, the answer that the review book gives favors a product that is more kinetically favored. I guess 1-butene would produce faster but if time allows, wouldn't it convert to a more thermodynamically favored product? Could anyone explain? Thank you
 
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  • #2
In order for a reaction to be thermodynamically favored, it must be reversible. This reaction, I believe, isn't, so you would use the more favored product.

Also, neither of the 2-butenes appears in the multiple choice question, methinks...
 
  • #3
If you use a very strong acid and choose the conditions properly, you can see rearrangement but that would likely lead to addition side reactions as well. Usually dehydration reactions are performed to maximize the actual dehydration without leading to further reactions, though. Beta elimination of the proton is very fast and leads to the alpha olefin under most condtions used for dehydration (ie. acid not too strong and acid's counterion not too good a nucleophile, etc...).

When you hear the sound of galloping hooves, think "Horses!" not zebras...
 

1. What is the difference between organic and inorganic chemistry?

Organic chemistry is the study of carbon-containing compounds, while inorganic chemistry focuses on non-carbon-containing compounds. Organic compounds are typically found in living organisms and are essential for life, while inorganic compounds can be found in non-living matter such as minerals and gases.

2. What are the main topics covered in organic chemistry?

The main topics in organic chemistry include the structure and properties of organic compounds, reactions and mechanisms, stereochemistry, and synthesis of organic molecules. Other important areas of study include biochemistry, pharmaceuticals, and materials science.

3. How is organic chemistry used in everyday life?

Organic chemistry is used in many aspects of daily life, including food and agriculture, medicine and healthcare, cosmetics and personal care products, and the production of materials such as plastics and textiles. It also plays a crucial role in environmental science and sustainability efforts.

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Organic chemistry is essential in the medical field as it helps us understand the structure and function of biological molecules in the human body. It is also crucial in the development of new drugs and treatments for various diseases and conditions, as well as in the analysis and detection of toxins and drugs in the body.

5. How can I prepare for organic chemistry questions on the MCAT?

To prepare for organic chemistry questions on the MCAT, it is important to have a strong understanding of the fundamental concepts and reactions in organic chemistry. Practice problems and review materials, such as textbooks and study guides, can also help you familiarize yourself with the types of questions that may be asked on the exam. Additionally, seeking out resources such as tutors or study groups can also aid in your preparation.

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