Essential Chemistry 2 ~ LECTURE NOTES WEEK ONE: INTRODUCTION TO ORGANIC CHEMISTRY What is organic chemistry? •
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Studies the properties, structure and reactions of covalent molecules based on carbon (and other non-­‐metal atoms) Chemistry of the elements on the right of the periodic table Found in: industry, consumer products, biochemistry Why are carbon compounds so important? •
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All living things are made up of carbon compounds. All the processes that happen in living things – digestion, movement, growth etc. – are chemical reactions involving carbon compounds. It is the ability of carbon to make so many different compounds that results in the rich diversity of life on earth The most important elements to join with carbon are hydrogen, oxygen and nitrogen. Carbon atoms can form chains of just carbon and hydrogen, which are called hydrocarbons. They can also form rings of carbon, called aromatics The carbon industry is one of the largest and most important industries because so many products contain organic compounds. Review of bonding compounds •
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An atom is a dense nucleus composed of protons (p+) and neutrons (n), surrounded by a cloud of electrons (e-­‐). A bond forms when one electron from each atom is shared with the other atom The interaction between the electrons of atoms within each molecule leads to covalent bonding between the atoms Electronegativity is the ability of an atom to pull electrons to it in a covalent bond. Higher electronegativity draws covalent bonding to it and forms partial charges Polar bonds exist when the bond is between atoms with different electronegativity. Partial positive and partial negative charges are on atoms of a polar bond. Non-­‐polar bonds are when there are no partial charges on the atoms. Polar bonds are very reactive. Molecular polarity determines physical and chemical properties. Atoms and molecules may be represented using the electron cloud model, the space-­‐filling model, the ball and stick model or its structural formula Atoms differ in the number of bonds they form Each atom has four pairs of electrons: a filled valence shell of electrons, bonding pairs and lone pairs Types of bonds: 1. Single: 1 covalent between atoms or 1 pair of electrons between atoms 2. Double: 2 pairs of electrons between atoms 3. Triple: 3 pairs of electrons between atoms Connectivity between atoms •
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Properties depend on structure How atoms are bonded: type of bond and relative electronegativity between atoms Functional group: patterns in structures that enable physical and chemical behaviour to be predicted Carbon backbone: inert Spectroscopy is a method of finding out about the structure of molecules that depends on the interaction of molecular compounds with radiation. When a molecular compound is exposed to electromagnetic radiation with a range of frequencies, it absorbs some or all of certain frequencies, but transmits radiations of other frequencies. The absorption of electromagnetic radiation causes different effects on molecular compounds, depending on the energy of the radiation and the molecular structure of the substance. -­‐ Mass spectroscopy involves breaking a molecule up and examining the mass of the fragments produced -­‐ IR spectroscopy involves exposing molecules to infrared radiation and observing what frequencies are absorbed -­‐ 13C NMR reveals carbon atoms in molecules in different bonding environments Isomers – Constitutional and Stereoisomers •
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Isomers have the same numbers and kinds of atoms but differ in the way the atoms are arranged Compounds like butane and 2-­‐methylpropane, whose atoms are connected differently, are called constitutional isomers Two molecules are described as stereoisomers of each other if they are made of the same atoms, connected in the same sequence, but the atoms are positioned differently in space. The difference between two stereoisomers can only be seen when the 3D arrangement of the molecules is considered.