From chemistry-request@server.ccl.net Tue Jul 20 11:07:11 1999 Received: from ccl.net (atlantis.ccl.net [192.148.249.4]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id LAA02750 for ; Tue, 20 Jul 1999 11:07:11 -0400 Received: from gatekeeper.es.dupont.com (gatekeeper.es.dupont.com [192.26.233.2]) by ccl.net (8.8.6/8.8.6/OSC 1.1) with ESMTP id KAA05445 for ; Tue, 20 Jul 1999 10:58:57 -0400 (EDT) From: fredvc@esalp1.dnet.dupont.com Received: from ns1-tmp.es.dupont.com (ns1-tmp.es.dupont.com [138.196.90.14]) by gatekeeper.es.dupont.com (8.9.3/8.9.3) with SMTP id KAA00190 for ; Tue, 20 Jul 1999 10:58:12 -0400 (EDT) Received: by ns1-tmp.es.dupont.com; id AA17671; Tue, 20 Jul 99 10:57:22 -0400 Message-Id: <9907201457.AA17671@ns1-tmp.es.dupont.com> Received: from esalp1.dnet; by esds01.dnet; Tue, 20 Jul 99 10:58:12 EDT Date: Tue, 20 Jul 99 10:58:12 EDT To: chemistry@ccl.net Cc: fredvc@esalp1.dnet.dupont.com Subject: RE: CCL: GEOMETRY QUESTION The problem outlined below was recently proposed to the list for comment: Given a fragment A-B-C, one wishes to attach a fourth atom, D, with the available information being: r(BD) <(ABD) <(CBD) how can one *uniquely* define the coordinates of D?? There is not enough information to define D uniquely. Consider the situation with the ABC fragment is constrained to the xy-plane: A / D--B \ C Unless the angles <(ABC), <(ABD), & <(CBD) sum to 360 deg., ther will be 2 solutions for the coordinates of D, differing in the algebraic sign for the z-coordinate. In order to uniquely locate D one needs one additional piece of information. Two possibilities are: out-of-plane angle (signed) for the BD bond dihedral angle A-C-B-D (signed) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ FREDERIC A. VAN-CATLEDGE Sr. Research Associate Scientific Computing Division || Office: (302) 695-1187 or 529-2076 Central Research & Development Dept. || The DuPont Company || FAX: (302) 695-9658 P. O. Box 80320 || Wilmington DE 19880-0320 || Internet: fredvc@esvax.dnet.dupont.com -------------------------------------------------------------------------------- Opinions expressed in this electronic message should ***> NOT <*** be taken to represent the official position(s) of the DuPont Company. *****> ANY OPINIONS EXPRESSED ARE THE PERSONAL VIEWS OF THE AUTHOR ONLY. <***** ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++