W2013CHM2311 Part 3a Notes

Staggered conforma0on of ethane c2h6 h3 h2 h4 h6 c h5

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: d σv : mirror planes that include the principal axis of rota+on. can some0mes be difficult as the defini0ons given are not (The subscript “v” is for “ver0cal”) σd : similar to σv however, this represents a special class of mirror always adhered to. plane that bisects two Cn axes. Don’t be too concerned with (The subscript “d” is for “dihedral”) dis0nguishing the two Example: Water has two σv mirror planes. σ H O H One mirror plane contains molecule. H C2 σ σv O H O A second mirror plane bisects molecule. Example: What kind of planes for benzene? H σv H Inversion Opera0on: i Each point moves through the center of the object to a posi0on opposite the original posi0on and as far from the central point as where it started. Staggered conforma0on of ethane (C2H6): H3 H2 H4 H6 C H5 i C H5 H1 H4 H1 C C H2 H6 H3 Methane (CH4): NO inversion center! H2 H1 i C H4 H3 H3 H4 H1 C H2 Improper Rota0on: Sn An improper rota0on consists of a rota0on of 360/n degrees followed by reflec0on through a plane perpendicular to the axis of the rota0on. Also referred to as a rota0on ­ reflec0on opera0on. Example: S4 in methane 1.  Rotate by 90° (=360°/4) 2.  Reflect through the mirror plane perpendicular to the rota0on axis H H C H H C4 H H Looking down C2 axis coincident with the S4 axis. C H H H σh H C H Initial and final stages are equivalent, even though intermediate stage differs. Cn NOTE: neither the C4 nor the σh are symmetry opera0ons for and σh sufficient but n methane but combined as an improper rota0on opera0on it is. ot necessary. H Improper Rota0on: Sn Another view of the S4 in methane: S4 H2 H1 C4 C H4 H3 H4 H1 H2 H4 σh C H3 H3 C H1 H2 Improper Rota0on: Sn A second S4 opera0on can be performed: S4 H4 H3 C4 C H1 H2 H1 H3 H4 H1 σh C H2 C H3 H2 H4 In General: Two successive Sn opera0ons generate the same result as a Cn/2 opera0on (S2n = Cn/2) S1 is the same as reflec0on (σ): In this case, call it σ rather than S1 S2 is the same as inversion (i): In this case, call it i rather than S2 When a symmetry opera0on yields the same result as a simpler opera0on (e.g., Snm = i or Cnm or σh), it is [email protected] as the simpler opera0on. Summary of Symmetry Elements and Opera0ons Symmetry Element Symbol Symmetry Opera.on Iden0ty E Leave the molecule alone Proper Axis Cn Rotate the molecule by 360/n degrees around the axis Horizontal Plane σh Reflect the molecule through the plane which is perpendicular to the principal axis Ver0cal Plane σv Reflect the molecule through a plane which contains the principal axis Dihedral Plane σd Reflect the molecule through a p...
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