From toukie@zui.unizh.ch Sun Jan 19 05:17:20 1997 Received: from rzusuntk.unizh.ch for toukie@zui.unizh.ch by www.ccl.net (8.8.3/950822.1) id EAA16984; Sun, 19 Jan 1997 04:26:07 -0500 (EST) Received: from rzurs3.unizh.ch by rzusuntk.unizh.ch (4.1/SMI-4.1.14) id AA07382; Sun, 19 Jan 97 09:59:37 +0100 Received: by rzurs3.unizh.ch (AIX 3.2/UCB 5.64/4.03) id AA66838; Sun, 19 Jan 1997 10:25:53 +0100 From: "Dr. S. Shapiro" Message-Id: <9701190925.AA66838@rzurs3.unizh.ch> Subject: ? re competing H-bonds To: chemistry@www.ccl.net Date: Sun, 19 Jan 1997 10:25:52 +0100 (MET) Cc: toukie@zui.unizh.ch X-Mailer: ELM [version 2.4 PL25 PGP2] Content-Type: text Forwarded message: > From toukie@zui.unizh.ch Thu Jan 16 12:13:27 1997 > Message-Id: <1.5.4.32.19970116111455.006763d0@zui.unizh.ch> > X-Sender: toukie@zui.unizh.ch (Unverified) > X-Mailer: Windows Eudora Light Version 1.5.4 (32) > Mime-Version: 1.0 > Content-Type: text/plain; charset="us-ascii" > Date: Thu, 16 Jan 1997 12:14:55 +0100 > To: chemistry@www.ccl.net > From: "Hr. Dr. S. Shapiro" > Subject: ? re competing H-bonds > Cc: toukie@zui.unizh.ch > > Dear Colleagues; > > A question has arisen here about hydrogen bonds for which I haven't > a clear answer. Perhaps someone knowledgable on this subject who reads this > list can help me. > > Consider an isolated phenolic hydroxy group; depending upon the > other molecules in its vicinity, it can either > > (a) form a hydrogen bond by donating its hydrogen atom to a nearby > hydrogen acceptor, or > > (b) form a hydrogen bond by donating the electrons on the oxygen > atom to a nearby hydrogen atom, or > > (c) both (a) and (b). > > Will the strength of the hydrogen bond formed between the oxygen > atom of the phenolic hydroxy moiety and a nearby hydrogen atom be weaker > than it might otherwise be if, at the same time, this phenolic hydroxy group > also donates it hydrogen atom in a second hydrogen bond? > > In other words, will the Ar-O --- H-R hydrogen bond in > | > H > > > Ar-O-H > | > | > | > H-R > > > be stronger than ther corresponding Ar-O --- H-R hydrogen bond in > | > H > > > Ar-O-H---O=C-R > | > | > | > H-R ? > > > > Thanks in advance to all responders. > > > Sincerely, > > S. Shapiro > ZH > toukie@zui.unizh.ch > > From KESKEJM@msn.com Sun Jan 19 13:17:30 1997 Received: from upsmot01.msn.com for KESKEJM@msn.com by www.ccl.net (8.8.3/950822.1) id MAA18209; Sun, 19 Jan 1997 12:20:28 -0500 (EST) Received: from upmajb02.msn.com (upmajb02.msn.com [204.95.110.74]) by upsmot01.msn.com (8.6.8.1/Configuration 4) with SMTP id JAA21971 for ; Sun, 19 Jan 1997 09:20:08 -0800 Date: Sun, 19 Jan 97 17:18:10 UT From: "Jonathan Keske" Message-Id: To: chemistry@www.ccl.net Subject: RE: ? re competing H-bonds The characterization of hydrogen bond interactions in phenolic systems would generally favour formation of hydrogen bonds with the phenolic hydrogen rather than the phenolic oxygen. This assumes that the proton affinity of the potential acceptor is greater than the phenol, e.g. water. The competitive difference between acceptance or donation of a hydrogen is around 4:1 in favour of donation with respect to water. The formation of a second hydrogen bond would tend to be weaker than it would otherwise be since the first hydrogen bond would reduce the electron density of the donor. In single hydrogen bond system one can relate the hydrogen bond interaction strength to differential proton affinity of the donor:acceptor pair. Jonathan M. Keske -----Original Message----- From: Computational Chemistry List On Behalf Of Dr. S. Shapiro Sent: Sunday, January 19, 1997 3:26 AM To: chemistry@www.ccl.net Cc: toukie@zui.unizh.ch Subject: CCL:? re competing H-bonds Forwarded message: > From toukie@zui.unizh.ch Thu Jan 16 12:13:27 1997 > Message-Id: <1.5.4.32.19970116111455.006763d0@zui.unizh.ch> > X-Sender: toukie@zui.unizh.ch (Unverified) > X-Mailer: Windows Eudora Light Version 1.5.4 (32) > Mime-Version: 1.0 > Content-Type: text/plain; charset="us-ascii" > Date: Thu, 16 Jan 1997 12:14:55 +0100 > To: chemistry@www.ccl.net > From: "Hr. Dr. S. Shapiro" > Subject: ? re competing H-bonds > Cc: toukie@zui.unizh.ch > > Dear Colleagues; > > A question has arisen here about hydrogen bonds for which I haven't > a clear answer. Perhaps someone knowledgable on this subject who reads this > list can help me. > > Consider an isolated phenolic hydroxy group; depending upon the > other molecules in its vicinity, it can either > > (a) form a hydrogen bond by donating its hydrogen atom to a nearby > hydrogen acceptor, or > > (b) form a hydrogen bond by donating the electrons on the oxygen > atom to a nearby hydrogen atom, or > > (c) both (a) and (b). > > Will the strength of the hydrogen bond formed between the oxygen > atom of the phenolic hydroxy moiety and a nearby hydrogen atom be weaker > than it might otherwise be if, at the same time, this phenolic hydroxy group > also donates it hydrogen atom in a second hydrogen bond? > > In other words, will the Ar-O --- H-R hydrogen bond in > | > H > > > Ar-O-H > | > | > | > H-R > > > be stronger than ther corresponding Ar-O --- H-R hydrogen bond in > | > H > > > Ar-O-H---O=C-R > | > | > | > H-R ? > > > > Thanks in advance to all responders.