Transcript Document
The study of carbon-based compounds and their properties. Historically the distinction between inorganic and organic substances was based on whether or not they were produced by living systems. It was believed that some sort of “life force” was needed to synthesize them. NH4OCN H2N—C—NH2 O urea In 1828, the German chemist Freidrich Wohler (1800-1882) prepared urea from the inorganic salt ammonium cyanate by simple heating. Hydrocarbons: contain only hydrogen and carbon Hydrocarbons can be divided into different types, depending on their bonding. Hydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes Cyclic Naming Organic Molecules Alkanes - - Carbon chain, no double or triple bonds. All single bonds (saturated) Alkenes - - Carbon chain, contains double bond(s) (unsaturated) Alkynes - - Carbon chain, contains triple bond(s) (unsaturated) Naming Organic Molecules There are two parts to the main name of each molecule… prefix: tells the # of carbons in main chain or ring suffix: tells the type of bonding in the chain or ring Prefix: indicates number of carbon atoms in the main chain or ring 1 meth- 6 hex- 2 eth- 7 hept- 3 prop- 8 oct- 4 but- 9 non- 5 pent- 10dec- Suffix: indicates types of bonds present Alkanes: (all single bonds) ___ -ane Alkenes: (double bond) ___ -ene Alkyne: (triple bond) ___ -yne Saturated v. Unsaturated fats Saturated with H Single bonds are free to rotate, so these fats can pack tightly (solid @ room temp) Which one is saturated? Saturated Hydrocarbons: the ALKANES: chains of carbon connected by single bonds: contain only single C-C bonds Have a general formula of CnH2n+2 ALKANES Methane, CH4 ALKANES Ethane, C2H6 Alkanes There are four ways to represent organic molecules: Structural formula: shows actual chemical structure Condensed formula: indicates structure through order of atoms Molecular formula: lists only number of each type of element Line formula: structural formula that assumes carbons as backbone and hydrogens to satisfy bonding needs Alkanes Structural Formula: Condensed Formula: CH3CH3 Molecular Formula: C2H6 Line Formula: ALKANES propane, C3H8 ALKANES butane, C4H10 ALKANES pentane, C5H12 ALKANES hexane, C6H14 ALKANES octane, C8H18 Don’t write this example down, but watch to see where we’re going with this… (Although you will be required to include the H’s if you take IB Chemistry) “Normal” v. Branched “normal” hydrocarbons are straight chains; no branching Branched-chain hydrocarbons – isomers of “normal” hydrocarbons; have same formula, but different structures “Normal” v. Branched When a side-chain exists, we name that functional group at the carbon where it is attached. Number carbons of main chain left to right Functional groups: (listed in alphabetical order) Methyl Ethyl Propyl Etc. -CH3 -CH2CH3 -CH2CH2CH3 n-butane 2-methylpropane n-pentane 2-methylbutane Are there any other pentane isomers? Another branched alkane: 2,2-dimethylpentane Cycloalkanes cyclopentane Cycloalkanes cyclobutane Cycloalkanes 1 -ethyl- 3 -methylcyclopentane ________________________ methyl3 1 green or red? 22 1 3 ethyl- Combustion and Halogenation of Alkanes Combustion of alkanes produces carbon dioxide and water. The only difference is the coefficients. Alkane + O2 CO2 + H2O E.g. CH3CH3 + 7O2 4CO2 + 6H2O Combustion and Halogenation of Alkanes Alkanes may react in the presence of a halogen in certain conditions (light, dark, heat) to produce a halogenated alkane and hydrogen gas. Alkane + halogen halogenated alkane + H2 E.g. CH4 + Br2 CH2Br2 + H2 Multiple isomers may exist Geometric Isomers How geometric isomers arise These isomers occur where you have restricted rotation somewhere in a molecule. At an introductory level in organic chemistry, examples usually just involve the carbon-carbon double bond Geometric Isomers E.g. 1,2-dichloroethane Is there more than one way of configuring this molecule? Nope. Let’s draw them. Geometric Isomers But what happens if you have a carboncarbon double bond - as in 1,2dichloroethene? Is there more than one isomer here? Yup. Let’s draw them. The possibility of an isomer here has to do with the double-bond. Geometric Isomers In one, the two chlorine atoms are locked on opposite sides of the double bond. This is known as the trans isomer. (trans : from latin meaning "across" - as in transatlantic). In the other, the two chlorine atoms are locked on the same side of the double bond. This is know as the cis isomer. (cis : from latin meaning "on this side") Unsaturated Hydrocarbons: ALKENES – contain C-C double bonds - have general formula of CnH2n 2-pentene Unsaturated Hydrocarbons: ALKENES 2,4-hexadiene Unsaturated Hydrocarbons: ALKYNES – contain C-C triple bonds - have general formula CnH2n-2 1-butyne Unsaturated Hydrocarbons: ALKYNES 3-ethyl-1-pentyne Aromatic Hydrocarbons: benzene – the simplest aromatic hydrocarbon; has a symmetrical ring structure (two structures depict resonance) Aromatic Hydrocarbons: benzene – can be drawn like this to show resonance (a way of describing electrons in cerntain molecules where bonding cannot be expressed in a single Lewis formula) Derivatives of benzene: 1-ethyl-2-methylbenzene Derivatives of benzene: 1,2-dimethyl-4-propylbenzene