W2013CHM2311 Part 3a Notes

D2h oxalate c2o42 o o c c o o 3c2 h 2 s2

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: them in this class) Low Symmetry Point Groups Group Symmetry C1 No symmetry other than the iden0ty opera0on Cs One mirror plane F Ci Only an inversion center One conformaLon H Cl Cl F H Assigning Point Groups Rules for Assigning Point Groups (cont’d): 4.  Does the molecule have any C2 axes perpendicular to the Cn axis? ↳  YES: D set of point groups; con0nue to step 5. ↳  NO: C or S set of point groups; con0nue to step 5. 5.  Does the molecule have a mirror plane (σh) perpendicular to the Cn axis? ↳  YES: classified as Cnh or Dnh. ↳  NO: C or S set of point groups; con0nue to step 6. 6.  Does the molecule have any mirror planes (σv or σd) that contain the Cn axis? ↳  YES: classified as Cnv or Dnd. ↳  NO: C or S set of point groups; con0nue to step 7. 7.  Is there an S2n axis collinear with the principal Cn axis? ↳  YES: classified as S2n. ↳  NO: classified as Cn. Flow Chart for Assigning Point Groups Highest Order Rota0on Axis Cn (n>1) YES Perpendicular C2’s? NO D Groups YES Dnh C or S2n Groups σh? σh? YES Dnd NO σd? YES NO Dn Cnh NO YES σv? Cnv NO YES S2n S2n? NO Cn Point Groups An equivalent flow ­chart: Are there n-C2 axes C n? NO nσ v Cnv C no σ Cn nσ d (S2n) σh Cnh Dn d YES D no σ Dn σh (& σv) Dn h Common Point Groups Cnv: very common point group; Cn axis + nσ planes containing Cn Cnh: Cn axis, σh (┴ Cn), Sn, and if n is even, i O F N N F H O B H O H C2h (has i) C3h (does not have i) Point Groups: D Classifica0on D Classifica.ons have Cn + nC2 axes (n ≥ 2) Dn : Not common; only Cn + nC2 (┴ Cn). Dnh: Quite common; Cn axis + nC2 axes (┴ Cn), σh (┴ Cn), n‑σ (containing Cn), Sn (automa0cally); if n even → i. D2h Oxalate, C2O42-: O O C C O O 3C2, σh, 2σ, "S2" ( = i). Different conventions for choosing "principal C2 axis. Cl D3h Cl D5 h B F F C3, 3σv, 3C2, σh, S3 Cl F Xe F F D6 h C6H6 Point Groups: D Classifica0on D Classifica.ons have Cn + nC2 axes (n ≥ 2) D∞h: Special Case; O=C=O C∞, S∞, ∞C2, ∞σv, σh, i Dnd: O~en hard to spot, Cn + nC2 (┴ Cn) + nσd + S2n. For n odd, have i. O~en the n ­C2 axes are hard to see – a good Lp ­off is the S2n axis coincident with Cn. D2d H C H Cl B C B C Cl Cl HH D3d Staggered C2H6: H H H C C H H H Cl N ote that they of ten look like C nv, but there is r eally more symmetry. R otate (90/n)º to see C 2 axes: D5d Fe Cl B Cl B Cl Cl Eclipsed D5h, intermediate, D5. Exercise – Assign a Point Group to each the following geometries Remember, molecular shape is based on nuclear framework (not LP’s) X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X...
View Full Document

This note was uploaded on 03/28/2014 for the course CHM 2311 taught by Professor Richardson during the Winter '09 term at University of Ottawa.

Ask a homework question - tutors are online