The major product obtained from the photocatalyzed bromination of 2-methylbutane is 1-bromo-2-methylbutane.
Understanding the Photocatalyzed Bromination of 2-Methylbutane
When discussing the "major product" of an organic compound like 2-methylbutane, it's crucial to specify the reaction it undergoes, as different reactions yield different products. In this specific case, we are focusing on its photocatalyzed bromination.
Mechanism of Free Radical Halogenation
Free radical halogenation, like bromination, is a common reaction for alkanes. It typically proceeds via a free radical chain mechanism involving three main steps:
- Initiation: A halogen molecule (e.g., Br₂) absorbs light energy (hv) and cleaves homolytically to form two highly reactive halogen radicals (Br•).
- Propagation:
- A halogen radical abstracts a hydrogen atom from the alkane, forming an alkyl radical and HX (e.g., HBr).
- The alkyl radical then reacts with another halogen molecule (Br₂), forming the bromoalkane product and regenerating a halogen radical (Br•), which continues the chain.
- Termination: Radicals combine with each other to end the chain reaction.
Bromination is known for its high selectivity compared to chlorination, meaning it preferentially substitutes hydrogen atoms at more stable radical positions (tertiary > secondary > primary).
Structure and Reactivity of 2-Methylbutane
2-Methylbutane is an alkane with the chemical formula C₅H₁₂. Its structure features different types of hydrogen atoms, which influences the possible products of bromination:
- Primary (1°) hydrogens: Located on carbon atoms bonded to only one other carbon atom.
- Secondary (2°) hydrogens: Located on carbon atoms bonded to two other carbon atoms.
- Tertiary (3°) hydrogens: Located on carbon atoms bonded to three other carbon atoms.
Let's break down the hydrogen types in 2-methylbutane:
CH3 (1°)
|
CH3 (1°) - CH (3°) - CH2 (2°) - CH3 (1°)- Six primary hydrogens: Three on the C1 methyl group, and three on the C4 methyl group. (Another three primary hydrogens are on the methyl group attached to C2).
- Two secondary hydrogens: On the C3 carbon.
- One tertiary hydrogen: On the C2 carbon.
Potential Bromination Products of 2-Methylbutane
Given the different types of hydrogens, bromination can lead to several monobrominated products, depending on which hydrogen atom is replaced by a bromine atom.
| Position of Bromination | Type of Hydrogen Removed | Resulting Product |
|---|---|---|
| C1 | Primary | 1-Bromo-2-methylbutane |
| C2 | Tertiary | 2-Bromo-2-methylbutane |
| C3 | Secondary | 2-Bromo-3-methylbutane |
| C4 | Primary | 1-Bromo-3-methylbutane |
The Major Product in Photocatalyzed Bromination
While standard free radical bromination typically favors the formation of products derived from the most stable radical (i.e., tertiary and then secondary bromoalkanes), under specific photocatalyzed conditions, the selectivity can sometimes vary.
For the photocatalyzed bromination of 2-methylbutane, the major product is identified as 1-bromo-2-methylbutane. This indicates that substitution occurred at a primary carbon atom (C1), leading to the formation of this specific isomer as the predominant product.
