Tertiary Hydrogens

Definition

Tertiary hydrogens refer to the hydrogen atoms bonded to a carbon atom that is connected to three other carbon atoms in an organic molecule. These hydrogens are considered tertiary because the carbon atom they are attached to has three other carbon atoms bonded to it, making it a tertiary carbon.

5 Must Know Facts For Your Next Test

1. Tertiary hydrogens are more reactive than primary or secondary hydrogens during radical halogenation reactions due to the increased stability of the resulting tertiary carbocation intermediate.
2. The presence of tertiary hydrogens in an alkane molecule can lead to the formation of multiple regioisomeric alkyl halides during the radical halogenation process.
3. Radical halogenation reactions involving tertiary hydrogens typically occur at a faster rate compared to reactions involving primary or secondary hydrogens.
4. The selectivity of radical halogenation reactions can be influenced by the relative abundance of tertiary, secondary, and primary hydrogens in the alkane substrate.
5. Tertiary hydrogens are more easily abstracted by halogen radicals during the initiation step of the radical halogenation mechanism, leading to the formation of tertiary carbocation intermediates.

Review Questions

• Explain the role of tertiary hydrogens in the radical halogenation of alkanes.
  • Tertiary hydrogens play a crucial role in the radical halogenation of alkanes. During the reaction, the halogen radicals preferentially abstract tertiary hydrogens, forming more stable tertiary carbocation intermediates. This increased stability of the tertiary carbocation makes the tertiary hydrogens more reactive compared to primary or secondary hydrogens, leading to a faster rate of reaction and the potential formation of multiple regioisomeric alkyl halide products.
• Describe how the presence of tertiary hydrogens can affect the selectivity of radical halogenation reactions.
  • The selectivity of radical halogenation reactions can be influenced by the relative abundance of tertiary, secondary, and primary hydrogens in the alkane substrate. Tertiary hydrogens are more easily abstracted by halogen radicals during the initiation step, leading to the formation of tertiary carbocation intermediates. These tertiary carbocations are more stable and, therefore, more likely to be involved in the subsequent substitution step, resulting in the formation of tertiary alkyl halides. The selectivity of the reaction can be tuned by controlling the relative amounts of tertiary, secondary, and primary hydrogens in the starting material.
• Analyze the implications of the increased reactivity of tertiary hydrogens in the context of radical halogenation reactions and the formation of alkyl halides.
  • The increased reactivity of tertiary hydrogens in radical halogenation reactions has several important implications. Firstly, it leads to the formation of more stable tertiary carbocation intermediates, which can then undergo substitution to produce tertiary alkyl halides. This can result in the generation of multiple regioisomeric products, as the halogen radical may abstract hydrogen from different tertiary positions within the alkane molecule. Additionally, the faster rate of reaction for tertiary hydrogens compared to primary or secondary hydrogens can impact the overall reaction kinetics and product distribution. Understanding the reactivity of tertiary hydrogens is crucial for predicting and controlling the outcomes of radical halogenation reactions, particularly when aiming to selectively produce specific alkyl halide products.

Related terms

Alkanes:

Saturated hydrocarbons with the general formula $C_nH_{2n+2}$, where each carbon atom is bonded to four other atoms, typically hydrogen.

Radical Halogenation:

A free-radical substitution reaction where a hydrogen atom in an alkane is replaced by a halogen atom (e.g., chlorine or bromine) to form an alkyl halide.

Tertiary Carbocation:

A positively charged intermediate formed during the radical halogenation of alkanes, where the positive charge is stabilized by the presence of three alkyl groups attached to the carbon atom.