Structure of Organic Compounds PDF

COLLEGE OF ENGINEERING Department of Mechanical and Industrial Engineering Structure of Organic Compounds Organic Chemistry (EME10313)  Lesson Plan Introduction The Carbon atom Catenation...

COLLEGE OF ENGINEERING Department of Mechanical and Industrial Engineering Structure of Organic Compounds Organic Chemistry (EME10313)  Lesson Plan Introduction The Carbon atom Catenation Classification of Carbon Atoms Orbital Structure of Atom Valency of carbon Types of Bonds Bonding in organic molecules Hybridization  Introduction to Carbon and its compound General structure of an atom (Ex. Carbon) 1. Outermost orbits are incomplete (except in nobel gases like He, Ne etc.) 2. Electrons in this orbit are called valence electrons. 3. Because of this incompleteness REACTIONS HAPPENS John McMurry. 2011. An introduction to Organic Chemistry. Cenagage Learning, New Delhi. PP 20-25. 3  Catenation and Valency of Carbon Ability to bond successively to other atoms to forms chains of varying lengths & shapes. (Catenation) Responsible for the variety & large number of organic compounds. Electronic Configuration: 2,4 Can gain 4 more electrons by forming 4 covalent bonds. Example: Methane CH4 John McMurry. 2011. An introduction to Organic Chemistry. Cenagage Learning, New Delhi. PP 18-19. 4 Classification of Carbon Atoms 5 Structures of few organic compounds 6  Chemical Bonds Ionic bond: transfer of valence electrons from one atom to another. Eg: NaCl Covalent bond ⮚ Nonpolar covalent bond: An even (nonpolar) distribution of charge between the atoms in a chemical bond. ⮚ Polar covalent bond is a covalent bond between atoms of different electronegativities. 7 8  Types of Covalent Bonds Sigma: Formed by linear or end to end overlap of orbitals. Strong bond. Like in methane all bonds are sigma. Pi: Formed by parallel or side by side overlap of p-orbitals. These are weaker than sigma bond. Like in ethylene one pi bond and one sigma bond. 9 Fig: The Electronegativities of Selected Elementsa 10  Test your understanding Which of the following has the most polar bond? Which of the following has the least polar bond? 11  Bond Length & Bond Energy Bond Length: The distance between the centers of the two nuclei. Unit: Angstrom Å Bond Energy: Amount of energy required to break a bond in a molecule. Unit: Kcal / mole Smaller the length, greater is the energy. 12 Distribution of Electrons in the First Four Shells That Surround the Nucleus The closer the orbital is to the nucleus, the lower is its energy. 13  Orbital Structure Shape & Size of the region in space around the nucleus, where the probability of finding an electron is maximum is called an Orbital. S- orbital: Spherical in shape P- orbitals: Three orbitals of dumb-bell shape of equal energy. 14  Formation of Covalent Bonds A covalent bond is formed when an orbital of an atom overlaps with the orbital of another atom; provided – ⮚ Two combining orbitals are half filled. ⮚ Electrons in the bonding orbitals have opposite spins. ⮚ Proper alignment of orbitals for effective overlap. wordpress.com 15  Hybridization Hybridization in plants is a common technique used in agriculture to create new plant varieties with desirable qualities. It involves crossing two different species or varieties of plants to produce a hybrid that combines characteristics from both parents. 16  Hybridization in Atoms Ground state carbon has two unpaired electron. But in excited state one of electron from 2s is promoted to vacant 2p orbital. Making space for 4 single bonds of different length & energy. But experimentally found all bonds of carbon are of same length and energy. It means 4 orbitals carrying single electrons got mixed and a new set of 4 orbitals was formed. 17  Hybridization in Atoms All new orbitals are same in energy, shape & size. Process of mixing of pure orbitals to produce a set of new equivalent orbitals is called as Hybridization. These new orbitals are called Hybrid orbitals. They make stronger bonds rather than pure atomic orbitals, because of greater overlapping. 18  sp3 Hybridization in Carbon 1. Each sp3 contains one electron. 2. It has 25% s-character and 75% p-character. 3. One small & one large lobe. 4. Identical in energy & shape but differ in orientation in space. 19  sp3 Hybridization in Carbon 4. All four lobes are directed towards the corners of a regular tetrahedron with carbon located at the center. 5. Angle between any two lobe is 109 028’. pinclipart.com 20  sp2 Hybridization in Carbon 1. Three sp2 orbitals arranged in trigonal planar geometry. 33% s & 66% p character. 2. Unmixed p-orbital is perpendicular to this plane. Later on it combine with p- orbital of another atom and give pi bond. 3. Bond angle between the hybrid orbitals is 1200. 21  sp Hybridization in Carbon 1. Two sp orbitals are 1800 apart from each other 2. 50% s-character & 50% p-character. 3. Two un-hybridized p-orbitals later combine to give two pi bonds perpendicular to each other. 22  Relative electronegativities of carbon atoms most electronegative→ sp > sp2 > sp3 ←least electronegative Effect of type of hybridization on electronegativity of the carbon atom In carbon atom s orbital closer to nucleus than p orbital Hence greater the s character of hybrid orbital, greater will be electronegativity. Sp – 50% s and 50% p character Sp2 – 33% s and 66% p character Sp3 – 25% s and 75% p character 23  Test your understanding 1. Arrange followings in ascending order of bond length : I. C-C II. C=C III. C ≡C 2. Why bond energy of C ≡C is greater than C=C bond? 3. Discuss the shape of acetylene molecule. 4. Analyze the energy associated with hybrid orbitals as compared to s and p orbital using an energy level diagram. 24