Question

Predict the order of acid strengths in the following series of cationic species: CH₃CH₂NH₃⁺,CH₃CH=NH₂⁺.​

a) CH₃CH=NH₂+ >CH ₃CH ₂NH3+
b) CH₃CH₂NH₃+>CH₃CH=NH₂+
c) They have equal strengths.
d) The order cannot be determined.

Answer 1

In the series CH3CH2NH3+ and CH3CH=NH2+, CH3CH2NH3+ is the stronger acid because its conjugate base is less stable, lacking the resonance stabilization that CH3CH=NH2+ has due to its double bond.

Step-by-step explanation:

The order of acid strengths in the series CH3CH2NH3+ and CH3CH=NH2+ can be predicted based on the stability of their conjugate bases after losing a proton. The conjugate base of CH3CH2NH3+ is CH3CH2NH2, and the conjugate base of CH3CH=NH2+ is CH3CH=NH. The presence of a double bond in CH3CH=NH allows for resonance stabilization, which makes it a more stable conjugate base compared to CH3CH2NH2. Therefore, CH3CH2NH3+ has a stronger acid because its conjugate base is less stable and it readily accepts a proton back. In light of this, the correct order is CH3CH2NH3+ > CH3CH=NH2+.