Competing nucleophiles
Experiment 5- Competing Nucleophiles
Table of results:
Area (mm²)
Percent composition
1-bromobutane
511
85.02%
1-chlorobutane
90
14.98%
2-bromobutane
432.25
78.63%
2-chlorobutane
117.5
21.37%
2-bromo-2-methylpropane
280
37.58%
2-chloro-2-methylpropane
465
62.42%
Discussion:
1. In 1-butanol
Base on the data table, 1-bromobutane dominated the composition of 85.02%, which indicates the conclusion that the mechanism for 1-butanol is SN2, and bromide is a better nucleophile. The first reason is that the substrate is a primary alcohol. The SN2 reaction is the nucleophilic attack of a central atom which kicks out the leaving group. A primary alcohol only has hydrogens plus the leaving group attached to the central carbon. Since the hydrogens do not hinder the nucleophilic attack, SN2 reaction is favored. The second reason is that bromide is a better nucleophile. Nucleophlicity is an essential factor in SN2 mechanism since the nucleophile is included in the rate determining step.
2. In 2-butanol
The results indicate that bromobutane dominated the composition of 78.63%, which means that the mechanism for 2-butanol was also SN2, and bromide is a better nucleophile. Due to the smaller percentage compared to 1-butanol, the mechanism of 2-butanol could either be a mixed between SN1 and SN2 because the substrate is a secondary alcohol. Bromide and chloride were both good nucleophiles, but bromide was the better nucleophile in 2-butanol as it yielded 78,63% of 2-bromobutane.
3. In 2-methyl-2-propanol
Since the substrate is a tertiary alcohol, SN1 should be favor regardless of the strength of nucleophiles. Tertiary alcohols are able to form very reactive carbocations that quickly combine with nucleophiles. This occurs much faster than the nuclephile attack of the substrate in Sn2 reactions because bulky methyl groups create steric hindrance and thus raise the activation energy for Sn2 reactions. Once formation of the carbocation
Table of results:
Area (mm²)
Percent composition
1-bromobutane
511
85.02%
1-chlorobutane
90
14.98%
2-bromobutane
432.25
78.63%
2-chlorobutane
117.5
21.37%
2-bromo-2-methylpropane
280
37.58%
2-chloro-2-methylpropane
465
62.42%
Discussion:
1. In 1-butanol
Base on the data table, 1-bromobutane dominated the composition of 85.02%, which indicates the conclusion that the mechanism for 1-butanol is SN2, and bromide is a better nucleophile. The first reason is that the substrate is a primary alcohol. The SN2 reaction is the nucleophilic attack of a central atom which kicks out the leaving group. A primary alcohol only has hydrogens plus the leaving group attached to the central carbon. Since the hydrogens do not hinder the nucleophilic attack, SN2 reaction is favored. The second reason is that bromide is a better nucleophile. Nucleophlicity is an essential factor in SN2 mechanism since the nucleophile is included in the rate determining step.
2. In 2-butanol
The results indicate that bromobutane dominated the composition of 78.63%, which means that the mechanism for 2-butanol was also SN2, and bromide is a better nucleophile. Due to the smaller percentage compared to 1-butanol, the mechanism of 2-butanol could either be a mixed between SN1 and SN2 because the substrate is a secondary alcohol. Bromide and chloride were both good nucleophiles, but bromide was the better nucleophile in 2-butanol as it yielded 78,63% of 2-bromobutane.
3. In 2-methyl-2-propanol
Since the substrate is a tertiary alcohol, SN1 should be favor regardless of the strength of nucleophiles. Tertiary alcohols are able to form very reactive carbocations that quickly combine with nucleophiles. This occurs much faster than the nuclephile attack of the substrate in Sn2 reactions because bulky methyl groups create steric hindrance and thus raise the activation energy for Sn2 reactions. Once formation of the carbocation