Textbook Problem 6.21

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Samantha Pedersen 2K
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Textbook Problem 6.21

Postby Samantha Pedersen 2K » Thu Dec 10, 2020 10:05 am

Problem 6.21 from the textbook says, "The two strands of the nucleic acid DNA are held together by hydrogen bonding between four organic bases. The structure of one of these bases, thymine, is shown below. c) Mark with an asterisk any structure that can show amphiprotic behavior in aqueous solution."

Image

The solutions manual says that the two nitro- groups can be amphiprotic. I understand that the nitrogen atoms can accept a proton, but how do we know that they can donate a proton? When they donate a proton, will they have 2 bonds and 2 lone pairs? Thank you!

Rich Luong 1D
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Re: Textbook Problem 6.21

Postby Rich Luong 1D » Thu Dec 10, 2020 4:11 pm

In this context, the two nitro- groups can accept and donate a proton because N has both a lone pair to accept an H+ and an H+ to give off. Usually when something is amphiprotic, it has both a H+ attached and some sort of charge to allow for H+ attachments. So yes, if the N does lose an H+, it will have two bonds and two lone pairs. I hope this helps!

kateraelDis1L
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Re: Textbook Problem 6.21

Postby kateraelDis1L » Thu Dec 10, 2020 6:36 pm

I have seen a pattern when asked to identify this type of question. That is that N bonded to 3 other things has the lone pair. So it is a site of attachment of a H+. So it can accept a proton. If given a huge lewis structure, ask yourself if there are lone pairs on the Nitrogens that you can "draw in".


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