Chemistry > Alkyl Halides and Aryl Halides > 8.0 Chemical Properties
Alkyl Halides and Aryl Halides
1.0 Alkyl halides
2.0 Halogen Derivatives of Unsaturated Hydrocarbons
3.0 Nomenclature
4.0 Isomerism
5.0 Nature of $C- X$ bond
6.0 Preparation
7.0 Physical Properties
8.0 Chemical Properties
9.0 Elimination Reactions
10.0 Reaction with Metals
11.0 Aryl Halides
12.0 Chemical Properties of Aryl Halides
13.0 Halogenation
14.0 Sulphonation
15.0 Nitration
16.0 Friedel-Craft's alkylation
17.0 Friedel Craft's acylation
8.1 $SN_1$ vs $SN_2$
| $SN_1$ | $SN_2$ | |
| Effect of nucleophile | Nucleophile strength is unimportant. | Strong nucleophiles are preferred. |
| Effect of substrate | Tertiary > Secondary > (Primary and methyl halides cannot easily undergo a reaction via this mechanism. (Tertiary halides can easily ionise and form carbocations.) | Methyl halide> Primary > Secondary. Tertiary halides do not undergo $SN_2$ substitution. (Primary and methyl halides are unhindered.) |
| Effect of solvents | Good ionising solvent is required. | Less polar solvent is preferred. |
| Rate of reaction | Dependent on the concentration of the substrate only. | Depends on both the concentration of the substrate and the nucleophile. |
| Stereochemistry | Reaction involves a flat carbocation intermediate that can be attacked from either side. This mechanism usually gives a mixture of products with inversion and retention of configuration. | Nucleophile attacks the back side of the substrate and thus completely inverts the stereochemistry of the carbon atom. |
| Rearrangements | Rearrangements can occur. (The intermediate carbocation can rearrange; alkyl shift or hydride shift can take place) | No rearrangement will take place. (Since the reaction takes place without the formation of an intermediate.) |
