1. 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 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 )

2. Chem 222 Spring 2013 2 How to determine point group symmetry H&S 3.1-3.4 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

3. Chem 222 Spring 2013 3 How to determine point group symmetry H&S 3.1-3.4 Example Is the molecule linear? NO Does the molecule have T d, O h or I h symmetry? YES  T d Example C3C3

4. Chem 222 Spring 2013 4 How to determine point group symmetry H&S 3.1-3.4 tetrahedron octahedron C3C3

5. Chem 222 Spring 2013 5 How to determine point group symmetry H&S 3.1-3.4 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

6. Chem 222 Spring 2013 6 How to determine point group symmetry H&S 3.1-3.4 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

7. Chem 222 Spring 2013 7 How to determine point group symmetry H&S 3.1-3.4 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

8. Chem 222 Spring 2013 8 How to determine point group symmetry H&S 3.1-3.4 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