Done by Shobana.N.S 1 BY SHOBANA.N.S QUEEN MARYS COLLEGE 2 Symmetry is present in nature and in human culture 3 Understand what orbitals are used in bonding. Predict optical activity of a molecule. Predict IR and Raman spectral activity 4 A molecule or object is said to possess a particular operation if that operation when applied leaves the molecule unchanged. 5 There are 5 kinds of operations 1. Identity 2. n-Fold Rotations 3. Reflection 4. Inversion 5. Improper n-Fold Rotation 6 IDENTITY E (Identity Operation) = no change in the object. Needed for mathematical completeness. Every molecule has at least this symmetry operation. 7 It is equal to rotation of the object 360/n degree about an axis. The symmetry element is line. Principle axis = axis with the largest possible n value. C n n Is equal to identity (E) 8 Symmetry element is plane. Linear object has infinite . v- plane including principle axis h- plane perpendicular to principle axis. d- plane bisecting the dihedral angle between two v plane. 9 (x,y,z) --> (-x,-y,-z). Symmetry element : point Symmetry operation : inversion through a point. i n is equal to identity (E) 10 It is also known as ROTATION-REFLECTION AXIS. Rotation followed by reflection. S n n = E ( n= even number) S n 2n = E ( n= odd number) 11 A symmetry element is a point of reference about which symmetry operations can take place Symmetry elements can be 1. point 2. axis and 3. plane 12 Symmetry element : point Symmetry operation : inversion 1,3-trans-disubstituted cyclobutane 13 Symmetry element : plane Symmetry operation : reflection 14 Symmetry element : line Symmetry operation : rotation 15 elementoperationsymbol symmetry planereflection through plane inversion center inversion: every point x,y,z translated to -x,-y,-z i proper axis rotation about axis by 360/n degrees CnCn improper axis 1. rotation by 360/n degrees 2. reflection through plane perpendicular to rotation axis SnSn 16 17 The collection of symmetry elements present in a molecule forms a group, typically called a POINT GROUP. The symmetry elements can combine only in a limited number of ways and these combinations are called the POINT GROUP. WHY IS IT CALLED A POINT GROUP?? Because all the symmetry elements (points, lines, and planes) will intersect at a single point. 18 19 C i has 2 symmetry operations : E the identity operation i point of inversion 20 C2H2F2Cl2 It has two symmetry operations E identity operation reflection 21 CH2BrCl 1- bromo, 2-chloro ethene Only one symmetry operation (E) Molecules in this group have no symmetry This means no symmetrical operations possible. 22 CHFBrCl Bromochlorofluoromethane Rotation of the molecule to 180 degree. This point group contains only two symmetry operations: E the identity operation C 2 a twofold symmetry axis Examples : water, chlorine trifluoride, hydrogen peroxide, formaldehyde 23 hydrazine 24 (2R,3R)-tartaric acidD-mannitol Rotation of the molecule to 120 degree. This point group contains only two symmetry operations: E the identity operation C 3 a three fold symmetry axis Examples: ammonia, boron trifluoride, triphenyl phosphine 25 26 9b H-Phenalene3,7,11-trimethyl cyclo dodeca 1,5,9-triene 2,6,7-trimethyl-1-aza-bicyclo [2.2.2]octane This point group contains the following symmetry operations E the identity operation C n n-fold symmetry axis. nv n reflection operation 27 This point group contains the following symmetry operations E the identity operation C 2 2-fold symmetry axis. 2v reflection operation 28 Examples: 1. Ozone 2. Thiophene 3. Furan 4. Pyridine 29 Sulphur dioxide Formaldehyde (Z)-1,2-DICHLORO ETHENE 30 m-Xylene Phenanthrene O-dichloro benzene p-dichloro benzene 31 32 Cyclohexane (boat) Water This point group contains the following symmetry operations E the identity operation C 3 3-fold symmetry axis. 3v reflection operation 33 Examples: 34 Ammonia POCl3 Trichloro methane Tert-butyl bromide This point group contains the following symmetry operations E the identity operation C 4 n-fold symmetry axis. 4v n reflection operation 35 36 EXAMPLES Xenon oxytetrafluoride Sulfur chloride pentafluoride Bromine pentafluoride Fluorine pentafluoride Calix[4]arene This point group contains the following symmetry operations E the identity operation C -fold symmetry axis. v n reflection operation 37 Linear Hetero nuclear Diatomic Molecule belongs to this category These molecules dont have centre of inversion. 38 Chloro ethyne This point group contains the following symmetry operations E the identity operation C n n-fold symmetry axis. h n reflection operation NOTE : If n is even i is present. 39 This point group contains the following symmetry operations E the identity operation C 2 2-fold symmetry axis. h reflection operation i inversion 40 41 EXAMPLES trans-1,2-dichloroethylene Trans-1,3-butadiene C2H2F2C2H2F2 N2F2 42 1,4-dibromo-2,5-dichloro-benzene(E)-1,2-dichloro ethene This point group contains the following symmetry operations E the identity operation C 3 3-fold symmetry axis. h reflection operation S3 improper axis of symmetry 43 44 Benzene-1,3,5-triol 45 This point group contains the following symmetry operations E the identity operation C n n-fold symmetry axis. nC 2 2-fold symmetry axis. (perpendicular to C n ) 46 This point group contains the following symmetry operations E the identity operation C 2 n-fold symmetry axis. 2C 2 2-fold symmetry axis. 47 twistan e 48 This point group contains the following symmetry operations E the identity operation C 3 3-fold symmetry axis. 3C 2 2-fold symmetry axis. 49 Ru(en)3 Perchlorotriphenylamine 50 Tris(oxalato)iron111 Molecular knot This point group contains the following symmetry operations E the identity operation C n n-fold symmetry axis. nC 2 2-fold symmetry axis. n d dihedral plane 51 NOTE : i is present when n is odd and S2n coincident to C2 axis This point group contains the following symmetry operations E the identity operation C 2 n-fold symmetry axis. 2C 2* 2-fold symmetry axis. 2 d dihedral plane 2S 4 improper axis of symmetry 52 53 allene (propa-1,2-diene)biphenyl 54 COT1,3,5,7- This point group contains the following symmetry operations E the identity operation C 3 n-fold symmetry axis. 2C 2 2-fold symmetry axis. 3 d dihedral plane 2S 6 improper axis of symmetry 55 56 Cyclohexane chair form 57 Ethane staggered form This point group contains the following symmetry operations E the identity operation 2C 4 n-fold symmetry axis. 4C 2* 2-fold symmetry axis. 4 d dihedral plane S 8 improper axis of symmetry C 2 2-fold symmetry axis. 58 Mn2(CO)10 This point group contains the following symmetry operations E the identity operation 4C 5 n-fold symmetry axis. 5C 2* 2-fold symmetry axis. 5 d dihedral plane S 10 improper axis of symmetry i inversion 59 60 This point group contains the following symmetry operations E the identity operation C n n-fold symmetry axis. nC 2 2-fold symmetry axis. h horizontal plane n v vertical plane S n improper axis of symmetry 61 62 This point group contains the following symmetry operations E the identity operation C 2 n-fold symmetry axis. 2C 2 2-fold symmetry axis. h horizontal plane 2 v vertical plane S 2 improper axis of symmetry 63 M2F6 ETHENE DIBORANE 64 65 1,4-DICHLOROBENZENE 66 [2,2] PARACYCLOPHANE 67 This point group contains the following symmetry operations E the identity operation C 3 3-fold symmetry axis. 3C 2 2-fold symmetry axis. h horizontal plane 2 v vertical plane 2S 3 improper axis of symmetry 68 69 cyclopropane 70 This point group contains the following symmetry operations E the identity operation C 4 4-fold symmetry axis. 4C 2 2-fold symmetry axis. h horizontal plane 4 v vertical plane S 4 improper axis of symmetry 71 Nickel tetracarbonyl 72 [AlCl]Xenon tetrafluoride 73 This point group contains the following symmetry operations E the identity operation C 5 4-fold symmetry axis. 5C 2 2-fold symmetry axis. h horizontal plane 5 v vertical plane S 5 improper axis of symmetry 74 75 This point group contains the following symmetry operations E the identity operation C 6 6-fold symmetry axis. 6C 2 2-fold symmetry axis. h horizontal plane 6 v vertical plane S 6 improper axis of symmetry i inversion 76 77 This point group contains the following symmetry operations E the identity operation C 4-fold symmetry axis. C 2 2-fold symmetry axis. h horizontal plane v vertical plane S improper axis of symmetry i inversion 78 POSSESS CENTER OF SYMMETRY 79 80 This point group contains the following symmetry operations E the identity operation 4C 3 3-fold symmetry axis. 3C 2 2-fold symmetry axis. 6 d dihedral plane 3S 4 improper axis of symmetry Total: 24 elements 81 METHANE 82 NEOPENTANE 83 This point group contains the following symmetry operations E the identity operation 3C 4 4-fold symmetry axis. 3C 2 2-fold symmetry axis. 3 h dihedral plane 3S 4 improper axis of symmetry i inversion C 3 3-fold symmetry axis S 6 improper axis of symmetry 6 C 2 2-fold symmetry axis. 6d dihedral plane TOTAL :48 elements 84 Cr(CO)6 [PtCl6]2- 85 PF6-CUBANE 86 SF6 87 This point group contains the following symmetry operations E the identity operation 20C 3 3-fold symmetry axis. 15C 2 2-fold symmetry axis. 15h horizontal plane 20S6 improper axis of symmetry i inversion 20C 3 3-fold symmetry axis 12S10 improper axis of symmetry 12C 5 5-fold symmetry axis. 12S10* improper axis of symmetry TOTAL : 120 elements 88 dodecahedran fullerenes 89