Test 2 7a

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Joseph Saba
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Joined: Thu Jul 11, 2019 12:16 am

Test 2 7a

Postby Joseph Saba » Tue Nov 26, 2019 12:27 pm

How do we know and determine the number of hydrogen bonds in Xanthin? I didn't know how to do this problem. Do we count the number of hydrogen bonds + the number of lone pairs?

Andrew F 2L
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Joined: Sat Aug 17, 2019 12:17 am

Re: Test 2 7a

Postby Andrew F 2L » Tue Nov 26, 2019 12:32 pm

Yes, you coun't the number of lone pairs and hydrogens and you should get 11 bonding sites. You may get 12 but my TA said that the Hydrogen that is on the most far right that is bonded to carbon cannot form a hydrogen bond because hydrogens need to bond to N O or F (or small molecules..) and since that hydrogen is bonded to a Carbon, it cannot bond to anything else with hydrogen bonds

Justin Quan 4I
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Joined: Sat Sep 14, 2019 12:17 am

Re: Test 2 7a

Postby Justin Quan 4I » Wed Nov 27, 2019 11:48 am

To add on, you should count the number of lone pairs on N, O, F atoms, plus the number of positively charged hydrogen atoms. You can tell if a hydrogen atom is positivity charged if it is bonding to another atom with a significant difference in electronegativity, like N, O, or F.

Matthew ILG 1L
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Joined: Sat Aug 17, 2019 12:15 am

Re: Test 2 7a

Postby Matthew ILG 1L » Wed Nov 27, 2019 4:43 pm

Andrew F 3B wrote:Yes, you coun't the number of lone pairs and hydrogens and you should get 11 bonding sites. You may get 12 but my TA said that the Hydrogen that is on the most far right that is bonded to carbon cannot form a hydrogen bond because hydrogens need to bond to N O or F (or small molecules..) and since that hydrogen is bonded to a Carbon, it cannot bond to anything else with hydrogen bonds

Why are the H-bonds included when counting? Can't hydrogen atoms only form one bond, so how would they still be included as a possible h-bond location?

Abigail Sanders 1E
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Joined: Wed Sep 11, 2019 12:16 am

Re: Test 2 7a

Postby Abigail Sanders 1E » Wed Nov 27, 2019 6:01 pm

H are included in possible hydrogen bond locations if they are bound to N, O, or F. Because they are bound to these atoms, hydrogen has a slightly positive charge due to the other atoms high electronegativity. Thus a hydrogen bond can form between a slightly negative O, N or F on another molecule and H on the original molecule. This can occur, remember, as it is not an actual bond but an intermolecular attractive force.

Jorge Ramirez_4H
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Joined: Wed Nov 21, 2018 12:19 am

Re: Test 2 7a

Postby Jorge Ramirez_4H » Wed Nov 27, 2019 8:12 pm

Wait, I thought that it was one bonding site. Why do the lone pairs count I thought it explicitly needed to show H bonding to F,O, or N.

Joseph Saba
Posts: 154
Joined: Thu Jul 11, 2019 12:16 am

Re: Test 2 7a

Postby Joseph Saba » Mon Dec 02, 2019 6:53 pm

Jorge Ramirez_4H wrote:Wait, I thought that it was one bonding site. Why do the lone pairs count I thought it explicitly needed to show H bonding to F,O, or N.

Lone pairs count because the resulting shape (trigonal pyramidal, tetrahedral, etc.) may not cancel out the enlarged lone pair thus leaving a delta negative charge


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