lesson 6 - diagnosing reactions - part 5

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mcatacct1
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lesson 6 - diagnosing reactions - part 5

Post by mcatacct1 » Mon Jun 22, 2020 5:31 pm

EDGs will make the nitrogen atoms more basic, and predict this trend, which is true in gaseous phase but no in the acqueous phase."

Why is this not true in the gaseous phase?
NS_Tutor_Nancy
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Re: lesson 6 - diagnosing reactions - part 5

Post by NS_Tutor_Nancy » Thu Jun 25, 2020 11:13 am

Hey, great question! This can be a confusing concept for a lot of students.

In the gas phase, the basicity trend is as shown in the video: NH3 < R-NH2 < R2-NH < R3-N

However, in the aqueous phase this trend changes slightly to: NH3 < R3-N < R-NH2 < R2-NH

The reason for the change is due to solvation effects. In an aqueous solution, primary (R-NH2) and secondary (R2-NH) amines are able to hydrogen bond to a much greater degree than tertiary amines (R3-N). This solvation effect / hydrogen bonding increases the electron density, thereby increasing the basicity.

I hope that helps!
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