Chapter Eleven: Introduction to Organic Chemistry organic chemistry: the study of compounds that contain the element carbon organic chemicals affect virtually every facet of our lives. products such as clothes, foods, medicines, gasoline, refrigerants, and soaps are composed almost solely of organic compounds. some organic products can be obtained directly from natural sources - cotton, wool, and silk. others can be synthetically produced - nylon and polyester. Characteristics of Organic Compounds some examples of organic compounds: • methane is the main component of natural gas. • ethanol is the alcohol present in alcoholic beverages. • capsaicin is responsible for the spiciness of peppers and is used for topical painrelief medicines. • caffeine is the stimulant found in coffee, tea, cola beverages, and chocolate. all organic compounds contain carbon atoms, and most contain hydrogen atoms: • carbon always forms four covalent bonds. • hydrogen always forms one covalent bond. carbon forms single, double, and triple bonds to other carbon atoms. some compounds have chains of atoms, and some compounds have rings. organic compounds may also contain elements other than carbon and hydrogen. • any atom that is not carbon or hydrogen is called a heteroatom. • each heteroatom forms a characteristic number of bonds, determined by its location in the periodic table. • the common heteroatoms (N, O, F, Cl, Br, and I) also have nonbonding, lone pairs of electrons, so that each atom is surrounded by an octet of electrons. • number of bonds + number of lone pairs = 4 the most common multiple bond between carbon and a heteroatom is a carbon-oxygen double bond. Shapes of Organic Molecules VSEPR (valence shell electron pair repulsion) theory: the most stable arrangement keeps the groups on a central atom as far away from each other as possible. • an atom surrounded by two groups is linear and has a bond angle of 180° • an atom surrounded by three groups is trigonal planar and has a bond angle of 120 ° • an atom surrounded by four groups is tetrahedral and has bond angles 109.5°. to draw a 3d tetrahedron on a page, we use: • a solid line for bonds in the plane • a wedge for a bond in front of the plane • a dashed line for a bond behind the plane every carbon with four single bonds is tetrahedral. nitrogen is attached to 3 atoms and has 1 lone pair, making its shape a trigonal pyramid. oxygen is attached to 2 atoms and has 2 lone pairs, making its shape bent. Drawing Organic Molecules - Condensed Structures in a condensed structure, all of the atoms are drawn in, but the twoelectron bond lines and lone pairs on heteroatoms are generally omitted. • a carbon bonded to 3 H’s becomes CH3 • a carbon bonded to 2 H’s becomes CH2 • a carbon bonded to 1 H becomes CH some bond lines can be drawn in for effect or to show specific bonding. identical groups can be condensed further: ex: convert each compound into a condensed structure: solution: Skeletal Structures when drawing a skeletal structure: • assume there is a carbon atom at the junction of any two lines or at the end of any line • assume there are enough hydrogens around each carbon to give it four bonds • draw in all heteroatoms and the hydrogens directly bonded to them Functional Groups functional group: an atom or group of atoms with characteristic chemical and physical properties a functional group contains a heteroatom, a multiple bond, or sometimes both. the letter R is used to abbreviate the carbon and hydrogen portion of a molecule. Hydrocarbons hydrocarbons: compounds that contain only carbon and hydrogen • alkanes have only C-C single bonds and no functional group. • alkenes have a C-C double bond as their functional group. • alkynes have a C-C triple bond as their functional group. • aromatic hydrocarbons contain a benzene ring, a six-membered ring with three double bonds. Compounds Containing a Single Bond to a Heteroatom Compounds Containing a C=O Group carbonyl groups (carbon-oxygen double bonds) are present in several different compounds an aldehyde contains a hydrogen atom directly bonded to the carbonyl carbon. a carboxylic acid contains an OH group directly bonded to the carbonyl carbon. an ester contains an OR group directly bonded to the carbonyl carbon . ex: identify all of the functional groups in the antiviral drug tamiflu. solution: redraw tamiflu to further clarify the functional groups: • tamiflu contains a total of five functional groups: a carbon-carbon double bond (an alkene), ether, ester, amide, and amine. • note the difference between an amine and an amide. an amine contains a N atom but no C=O. an amide contains an N atom bonded directly to a C=O. Properties of Organic Compounds organic compounds are composed of covalent bonds only. organic compounds exist as discrete molecules with much weaker intermolecular forces than those seen in ionic compounds. as a result, organic compounds have lower boiling points and melting points than ionic compounds. organic compounds tend to be liquids or gases at room temperature, while ionic compounds are solids. Polarity a covalent bond is nonpolar when two atoms of identical or similar electronegativity are bonded. thus, C-C and C-H bonds are nonpolar bonds. a covalent bond is polar when atoms of different electronegativity are bonded thus, bonds between C and N, O, and the halogens are polar bonds. hydrocarbons contain only if a single bond is polar, the nonpolar C-C and C-H bonds, so molecule is polar because it they are nonpolar molecules. contains a net dipole. if the individual polar bonds if the individual bond dipoles do not (dipoles) cancel in a molecule, the cancel, the molecule is polar. molecule is nonpolar. ex: explain why CH2Cl2 is a polar molecule. solution: Solubility the rule of solubility is “like dissolves like.” most organic compounds are soluble in organic solvents. hydrocarbons and other nonpolar organic compounds are insoluble in water. polar organic compounds are water soluble only if they are small and contain a N or O atom that can hydrogen bond with water. small nonpolar molecule; no O or N small polar molecule O atom present, so it is H2O insoluble. present, so it is H2O soluble. very large molecule O atom present too many nonpolar C-C and C-H bonds H2O insoluble Focus on Health and Medicine: Vitamins vitamins: organic compounds needed in small amounts for normal cell function. • the body cannot synthesize these compounds; they must be obtained in the diet. • a fat-soluble vitamin dissolves in an organic solvent but is insoluble in water. • fat-soluble vitamins have many nonpolar C-C and C-H bonds and few polar functional groups. • a water-soluble vitamin dissolves in water. • water-soluble vitamins have many polar bonds. Vitamin A vitamin A - retinol - is an essential component of the vision receptors in the eyes. it also helps to maintain the health of the mucous membranes and the skin. vitamin A is a very large, mostly nonpolar molecule with only one OH group, making it a fat-soluble vitamin. Vitamin C vitamin C - ascorbic acid - is important in the formation of collagen, the connective tissue of the skin. a deficiency in vitamin C causes scurvy, a condition of sailors in the 1600s who had no access to fresh fruit while at sea. it has many polar bonds and many O atoms, making it a water-soluble vitamin.

Chapter 11 - Introduction to Organic Chemistry

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