Chem 222 Spring 2013 1 How to determine point group symmetry H&S 3.1-3.4 Example: BF 3 Is the molecule linear? NO Does the molecule have T d, O h or I.

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Chem 222 Spring How to determine point group symmetry H&S Example: BF 3 Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? YES (C 3 ) Is there a C 2 axis perpendicular to the principal Cn? YES Is there a σ h (perpendicular to the principal Cn)? YES  The BF 3 molecule has D 3h symmetry (note we did not have to find ALL of the elements/operations for D 3h )

Chem 222 Spring How to determine point group symmetry H&S Example: CH 3 CN Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? YES (C 3 ) Is there a C 2 axis perpendicular to the principal Cn? NO Is there a σ h (perpendicular to the principal Cn)? NO  CH 3 CN belongs to the C 3V point group Is there a σ V (containing the principal Cn)? YES

Chem 222 Spring How to determine point group symmetry H&S Example Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? YES  T d Example C3C3

Chem 222 Spring How to determine point group symmetry H&S tetrahedron octahedron C3C3

Chem 222 Spring How to determine point group symmetry H&S Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? YES, C 3  C 3v Example C3C3 Is there a C 2 axis perpendicular to the principal Cn? NO Is there a σ h (perpendicular to the principal Cn)? NO Is there a σ V (containing the principal Cn)? YES

Chem 222 Spring How to determine point group symmetry H&S Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? YES (C 2 ) Is there a C 2 axis perpendicular to the principal Cn? NO Is there a σ h (perpendicular to the principal Cn)? NO  C 2v Is there a σ V (containing the principal Cn)? YES

Chem 222 Spring How to determine point group symmetry H&S Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? NO Is there a mirror plane? YES  C s

Chem 222 Spring How to determine point group symmetry H&S Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Clicker question: What point group does the following molecule belong? (a)C s (b) C 2 (c) C 2V (d) C 2h (e) D 2d Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? NO Is there a Cn axis? NO Is there a mirror plane? YES  C s