For each pair of compounds, state which compound is the better SN2 substrate. a. 2-methyl-1-iodopropane or tera-butyl iodide. b. cyclohexyl bromide or 1-bromo-1-methylcyclohexane

Verified step by step guidance

1. Identify the structure of each compound to understand the steric hindrance around the carbon atom bonded to the halide. Steric hindrance plays a crucial role in SN2 reactions as it can impede the approach of the nucleophile.
2. For pair (a), compare the steric hindrance of 2-methyl-1-iodopropane and tera-butyl iodide. Note that in SN2 reactions, less hindered (less bulky) substrates are more favorable as the nucleophile needs to attack the carbon atom bonded to the leaving group (iodide in this case).
3. For pair (b), analyze the structures of cyclohexyl bromide and 1-bromo-1-methylcyclohexane. Consider the impact of the methyl group in 1-bromo-1-methylcyclohexane on the accessibility of the carbon bonded to the bromine atom.
4. Determine which compound in each pair has the least steric hindrance around the carbon atom bonded to the halide. This compound will generally be the better SN2 substrate because it allows easier access for the nucleophile to perform the backside attack.
5. Conclude which compound in each pair is the better SN2 substrate based on the analysis of steric hindrance and accessibility of the carbon atom bonded to the halide.

Key Concepts

SN2 Mechanism

The SN2 mechanism is a type of nucleophilic substitution reaction where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction is characterized by a single concerted step, leading to an inversion of configuration at the carbon center. The rate of the reaction depends on both the concentration of the nucleophile and the substrate, making sterics and electronic factors crucial for determining the reactivity.

Steric Hindrance

Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In SN2 reactions, bulky groups around the electrophilic carbon can hinder the approach of the nucleophile, making the substrate less reactive. Therefore, substrates with less steric hindrance, such as primary or secondary alkyl halides, are generally better SN2 substrates compared to tertiary ones, which are often too hindered for effective nucleophilic attack.

Leaving Group Ability

The ability of a leaving group to depart from a substrate is a critical factor in determining the feasibility of an SN2 reaction. Good leaving groups, such as iodide and bromide, stabilize the negative charge after leaving, facilitating the reaction. In comparing substrates, the nature of the leaving group can influence the overall reaction rate, with better leaving groups enhancing the likelihood of successful nucleophilic substitution.