Consider the reaction of 1-bromobutane with a large excess of ammonia (NH3).
b. Draw the reactants, the transition state, and the products. Note that the initial product is the salt of an amine (RNH3+ Br−), which is deprotonated by the excess ammonia to give the amine.
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1
Draw the structure of 1-bromobutane, which is a four-carbon chain with a bromine atom attached to the first carbon.
Draw the structure of ammonia (NH3), which is a nitrogen atom bonded to three hydrogen atoms with a lone pair of electrons on the nitrogen.
Illustrate the nucleophilic substitution reaction (S_N2) where the lone pair on the nitrogen of ammonia attacks the carbon bonded to the bromine in 1-bromobutane, forming a transition state.
Show the formation of the initial product, which is the ammonium salt (RNH3+ Br−), where the nitrogen is now bonded to the butyl group and carries a positive charge.
Depict the deprotonation step where another molecule of ammonia acts as a base to remove a proton from the ammonium ion, resulting in the formation of the neutral amine (RNH2) and ammonium bromide (NH4+ Br−) as the final products.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophile, resulting in the replacement of a leaving group. In the case of 1-bromobutane reacting with ammonia, the ammonia acts as a nucleophile, attacking the carbon atom bonded to the bromine, leading to the formation of an amine and the release of bromide ion.
Nucleophiles and Electrophiles can react in Substitution Reactions.
Transition State
The transition state is a high-energy, unstable arrangement of atoms that occurs during a chemical reaction, representing the point at which reactants are transformed into products. It is crucial for understanding reaction mechanisms, as it provides insight into the energy barrier that must be overcome for the reaction to proceed. In this reaction, the transition state would involve the formation of a bond between the nitrogen of ammonia and the carbon of 1-bromobutane.
Deprotonation is the removal of a proton (H+) from a molecule, resulting in the formation of a base. In the context of the reaction described, after the initial formation of the ammonium salt (RNH3+ Br−), the excess ammonia acts to deprotonate the ammonium ion, yielding the neutral amine. This step is essential for achieving the final product and illustrates the role of ammonia as both a nucleophile and a base.