Basics in Organic Reactions Mechanisms
In organic chemistry, the mechanism of an organic reaction is defined as a complete step-by-step explanation of how a reaction of organic compounds happens. A completely detailed mechanism would relate the first structure of the reactants with the last structure of the products and would represent changes in structure and energy all through the reaction step.
Heterolytic Bond Breaking
Heterolytic bond breaking is also known as heterolysis or heterolytic fission or ionic fission. It is defined as breaking of a covalent bond between two different atoms in which one atom gains both of the shared pair of electrons. The atom that gains both electrons is more electronegative than the other atom in covalent bond. The energy needed for heterolytic fission is called as heterolytic bond dissociation energy.
Polar Aprotic Solvent
Solvents that are chemically polar in nature and are not capable of hydrogen bonding (implying that a hydrogen atom directly linked with an electronegative atom is not found) are referred to as polar aprotic solvents. Some commonly used polar aprotic solvents are acetone, DMF, acetonitrile, DMSO, etc.
Oxygen Nucleophiles
Oxygen being an electron rich species with a lone pair electron, can act as a good nucleophile. Typically, oxygen nucleophiles can be found in these compounds- water, hydroxides and alcohols.
Carbon Nucleophiles
We are aware that carbon belongs to group IV and hence does not possess any lone pair of electrons. Implying that neutral carbon is not a nucleophile then how is carbon going to be nucleophilic? The answer to this is that when a carbon atom is attached to a metal (can be seen in the case of organometallic compounds), the metal atom develops a partial positive charge and carbon develops a partial negative charge, hence making carbon nucleophilic.
see the attached question and out of these 3 comounds, which one is the best dienophile ?
![**Hydrogenation Heat Liberation in Compound Pairs**
**Question:**
In each of the following pairs of compounds, circle the one which liberates most heat upon hydrogenation? Why?
**Pair a:**
Compound 1: Benzene
Compound 2: Cyclohexene
**Pair b:**
Compound 1: 1,3-Cyclohexadiene
Compound 2: 1,4-Cyclohexadiene
**Explanation:**
- Pair **a** features two compounds, benzene (a six-carbon ring with alternating double bonds) and cyclohexene (a six-carbon ring with one double bond).
- Pair **b** showcases two isomers of cyclohexadiene: 1,3-Cyclohexadiene (double bonds at positions 1 and 3) and 1,4-Cyclohexadiene (double bonds at positions 1 and 4).
The hydrogenation process involves the addition of hydrogen (H₂) to these compounds, converting double bonds to single bonds and liberating heat in the process. The amount of heat released is generally more significant for compounds with higher degrees of unsaturation (more double bonds) and less stability. For example, benzene is particularly stable due to aromaticity, whereas cyclohexene, having one double bond, would release more heat upon hydrogenation. Similarly, the stability of the diene will influence the heat of hydrogenation.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd4227bd0-1517-489e-a98f-d0498762017f%2F6bfc653d-8289-4ddd-9e38-e4e2b13cdd51%2Fk12h5f9_processed.png&w=3840&q=75)
![### Aromatic Ketones: Structural Representation
Aromatic ketones are organic compounds featuring a carbonyl group (C=O) directly bonded to an aromatic ring. Below are three structural representations of different aromatic ketones:
1. **Phenylacetone**
![Phenylacetone](https://vizhub.health.sydney.edu.au/wp-content/pictures/conversions/10038.edges/cyclophorogrin_clear.png)
- This compound consists of a benzene ring with a carbonyl group (C=O) attached directly to the ring.
2. **Cyclohexanone**
![Cyclohexanone](https://vizhub.health.sydney.edu.au/wp-content/pictures/conversions/10039.edges/cyclophorogrin_clear.png)
- Here, the carbonyl group (C=O) is attached to a six-membered cyclohexane ring, forming a cyclohexanone.
3. **Acetophenone**
![Acetophenone](https://vizhub.health.sydney.edu.au/wp-content/pictures/conversions/10040.edges/cyclophorogrin_clear.png)
- This molecule consists of a benzene ring with a carbonyl group (C=O) and an additional methyl group (CH₃) attached to it, resulting in acetophenone.
Each structurally represented molecule is a clear visual depiction of how the carbonyl functional group varies in attachment to either a benzene ring or a cyclohexane ring. Such representations aid in understanding the different structural forms and their nomenclature in aromatic ketones.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd4227bd0-1517-489e-a98f-d0498762017f%2F6bfc653d-8289-4ddd-9e38-e4e2b13cdd51%2F8wn9sf7_processed.png&w=3840&q=75)
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