Sn1 and Sn2 reaction mechanism

1. Sn1 and Sn2 reaction mechanism Mr. Fergason

2. Substitution reactions • Aqueous • Nucleophilic substitution • Nucleophile • Transition state(activated complex) • Primary Halogenoalkanes • Secondary Halogenoalkanes • Tertiary Halogenoalkanes • Hydrolysis • Heterolytic fission Vocabulary

3. There are three types of Halaogenoalkanes based upon how many carbons are attached to the carbon containing the halide. • Primary Halogenoalkanes have 1 carbon attached to the carbon containing the halide. • SecondaryHalogenoalkanes have 2 carbons attached to the carbon containing the halide. • TertiaryHalogenoalkanes have 3 carbons attached to the carbon containing the halide. Types of Halogenoalkanes

4. Remember, organic compounds are named with the lowest possible combination of numbers. • These coefficients in front represent the position of the halide on the carbon chain • Draw the following molecules • 3,4-dichlorohexane • 2-bromo-4-chloroctane Naming Halogenoalkanes

5. Halogenoalkanes are slightly soluble or insoluble in water. • As the molecular weight of the halogenoalkane increases, the boiling point increases. • Halides of similar alkanes have similar boiling points. Properties of Halogenoalkanes

6. The primary type of reaction undergone for halogenoalkanes is substitution. • A functional group, such as OH, is substituted for the halide in the carbon chain. • Most of these reaction occur in solution, aqueous, and are part of a hydrolysis reaction. • In a hydrolysis reaction, the molecule is broken apart by water. Mechanisms

7. The specific mechanism that occurs with primary, secondary, and tertiary halogenoalkanes is nucleophilic substitution. • A nucleophile is a negatively charged molecule or ion that has a lone pairs of electrons which is attracted to the positive portion of a molecule and donates these electrons to form a covalent bond. Mechanisms

8. This mechanism occurs with primary halogenoalkanes • During this mechnism, the nucleophile is substituted for the halide in the carbon chain. • Because the carbon can only have eight electrons, the nucleophile breaks the bond between the C and the halide causing both electrons to go back to the halide and forming an ion. • This process is known as heterolytic fission. • The illustration the book shows the transition state where both molecules are attached to the carbon chain at the same time. When this occurs, we are at the highest point on the energy curve which is sometimes referred to as the activated complex. Sn2 mechanism

9. The Sn1 mechanism occurs with tertiary halogenoalkanes. • It is a slower mechanism than the Sn2 mechanism and independent of concentration while the Sn2 mechanism is dependent on concentration. • The first step in this mechanism causes the halide to break away from the carbon chain causing a positively charged carbon chain. • The second step involves the nucleophilic substitution where the nucleophile is substituted in the place of the empty spot on the carbon chain. • The first step determines the rate of the reaction. • The Sn1 mechanism is considered to be a faster mechanism for the reaction of halgenoalkanes due to the polarity of water. Sn1 mechanism

10. Second halogenoalkanes undergo a mixture of the Sn1 and Sn2 reactions mechanism when reacting with sodium hydroxide. • These are not discussed heavily in SL chemistry. Secondary halogenoalkanes