Pharmaceutical Organic Chemistry I Lecture Notes PDF

Pharmaceutical Organic Chemistry I Prof. Dr. Omneya M. Khalil Vice Dean For Education and Student affairs, Faculty of Pharmacy, MTI University 1  Introduction 2  What is Hybridization? sis the concept of mixing atomic orbitals to form new hybrid ones sui...

Pharmaceutical Organic Chemistry I Prof. Dr. Omneya M. Khalil Vice Dean For Education and Student affairs, Faculty of Pharmacy, MTI University 1  Introduction 2  What is Hybridization? sis the concept of mixing atomic orbitals to form new hybrid ones suitable for the pairing of electrons to form chemical bonds. s Types of Hybridization S 1- sp3 2- sp2 3- sp 3 s 1- sp3 Hybridization: e.g. Methane CH4 Ground state (lowest energy state) for a neutral carbon ( 6C12) 1s2 2s2 2p2 How does the C form 4 bonds if it has only 2 half-filled p orbitals available for bonding? Answer: orbital hybridization Excited state by absorbing energy, electron configuration is 1s2 2s1 2p3 the 4 valence orbitals of the carbon (one 2s & three 2p orbitals) combine to form 4 equivalent hybrid orbitals, which are called sp3 orbitals 5 sp3 Hybridization: e.g. Methane CH4 3 dimensional space to minimize repulsion 6  Tetrahedral with bond angles of 109.5o 7 s 2- sp2 Hybridization: tetrahedral geometry which gives idealized bond angles of 109.3o. Open chain= aliphatic s orbital is mixed with only 2 p orbitals 8 s 2- sp2 Hybridization: tetrahedral geometry which gives idealized bond angles of 109.3o. 3 sp2 orbitals are arranged in a trigonal planar geometry (120o) 9 s 2- sp2 Hybridization: e.g. Ethylene C2H4 10 s 2- sp2 Hybridization: e.g. Ethylene C2H4 2 sp2 hybridized C atoms can make a sigma s bond by overlapping one of the 3 sp2 orbitals 2 H make sigma s bonds with each C by overlapping their s orbitals with the other 2 sp2 orbitals. which gives idealized bond angles of 109.3o. 11 s 2- sp2 Hybridization: The unhybridized 2p in both C’s are left available to form the double bond’s π bond (side-by-side overlap of 2 p orbitals). 12 2- sp2 Hybridization: 13 s 3- sp Hybridization: e.g. Acetylene C2H2 Involves the mixing of one s and one p orbital of an atom resulting in the formation of 2 new equivalent orbitals 14 15  Linear with bond angles of 180o 16  Difference between sp3, sp2 & sp Category sp3 sp2 sp Number of 4 3 2 Hybridized Orbitals Number of Zero 1 2 Unhybridized Orbitals Geometry Tetrahedral Trigonal Linear around planar Central Atom Bond Angle 109.5 120 180 around Central Atom (∘) 17 Single carbon–carbon (C–C) bonds are formed from one sigma bond (s) Double (C=C) bonds are formed from one sigma bond (s) and one π bond. Triple bonds are formed through the combination of one sigma bond (s) and two π bonds. 18  Electronegativity ( EN ) It is the ability of an atom to attract electrons. 19  Electronegativities of Selected Elements Li3 Be4 B5 C6 N7 O8 F9 1.0 1.57 2.0 2.55 3.04 3.44 4.0 Decrease in EN Increase in EN Cl17 3.16 Br35 2.96 I53 2.66 20  Types of chemical bonds According to the difference in EN between 2 atoms therefore we can determine the type of chemical bond. 21  Types of chemical bonds Ionic Covalent Difference in EN >2 Polar Non polar Difference in EN 2 It is the transfer of an electron from one atom to another e.g. Na+Cl- , K+Br- The atom that donates the electrons becomes +vely charged and called cation, while the atom which receives electrons becomes –vely charged and called anion. 23 Covalent bond: It is the sharing of electrons between 2 atoms. A- Non polar covalent bond : Difference in EN=0.5-zero The bond between 2 atoms of same EN e.g. C-C , Br-Br or near to each other e.g. C-H 24  B- Polar covalent bond: Formed when the difference in EN is