Organic Chemistry: Alkanes, Alkenes, and Hydrocarbons, Study notes of Chemistry

Download Organic Chemistry: Alkanes, Alkenes, and Hydrocarbons and more Study notes Chemistry in PDF only on Docsity! 1 22.1 Alkanes: Saturated Hydrocarbons 22.2 Alkenes and Alkynes 22.3 Aromatic Hydrocarbons 22.4 Hydrocarbon Derivatives 22.5 Polymers 22.6 Natural Polymers ← Biochemistry Chem 162A March 6 2006 Lecture/Jenekhe Chapter 22. Organic and Biochemical Molecules Computer model of a globular protein ORGANIC CHEMISTRY — The study of carbon-containing compounds and their properties (DOES NOT INCLUDE: CO, CO2, CO32- salts, etc.) • > 107 known organic compounds • Biomolecules and living systems • Synthetic fibers, plastics, rubbers, etc. • medicines (drugs) • food • energy fuel sources (petroleum, coal, natural gas) 2 22.1 Alkanes: Saturated Hydrocarbons • Hydrocarbons (compounds containing carbon + hydrogen) C C H H H H + H2 hydrogenation C C H H H H H H hydrocarbons Saturated (ie. alkanes) — all C-C bonds and single bonds Unsaturated — contain C=C or C≡C bonds ethylene (unsaturated) sp2 hybridized carbon ethane (saturated) sp3 hybridized carbon • Alkanes • general formula: CnH2n+2 normal (linear or straight-chain or unbranched) alkanes branched alkanes • H3C CH2 CH3n normal alkanes Figure 22.1: C-H bonds in methane 5 Figure 22.4: (a) normal butane (b) branched isomer Exercise 22.1 Structural Isomerism Draw the isomers of pentane. Solution Pentane (C5H12) has the following isomeric structures: 1. 2. 3. CH3-CH2-CH2-CH2-CH3 n-Pentane H3C CH CH3 CH2 CH3 Isopentane 6 Exercise 22.1 Structural Isomerism Draw the isomers of pentane. Solution Pentane (C5H12) has the following isomeric structures: 1. 2. 3. CH3-CH2-CH2-CH2-CH3 n-Pentane H3C CH CH3 CH2 CH3 Isopentane C CH3 CH3H3C CH3 Neopentane Pentane (a), Isopentane (b), and Neopentane (c) (a) (b) (c) 7 Naming Alkanes: Nomenclature CH3 CH2 CH2 CHH2CH3C CH2 CH3 six carbon Rules for Naming Alkanes 1. The names of the alkanes beyond butane are obtained by adding the suffix –ane to the Greek root for the number of carbon atoms (penta- for five, hex- for six, and so on). For a branched hydrocarbon, the longest continuous chain of carbon atoms determines the root name for the hydrocarbon. For example, in the alkane the longest chain contains six carbon atoms, and this compounds is named as a hexane. 2. When alkane group appear as substituents, they are named by dropping the –ane and adding –yl. For example, -CH3 is obtained by removing a hydrogen from methane and is called methyl, - C2H5 is called ethyl, -C3H7 is called propyl, and so on. The compound above is therefore an ethylhexane. (See Table 22.2.) R- group -CnH2n+1 e.g. –C6H13 (hexyl) Table 22.2 3. The positions of substituent groups are specified by numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching. For example, the compound is called 3-methylhexane. Note that the top set of numbers is correct since the left end of the molecule is closest to the branching, and this gives the smallest number for the position of the substituent. Also, note that a hyphen is written between the number and the substituent name. 4. The location and name of each substituent are followed by the root alkane name. The substituents are listed in alphabetical order, and the prefixes di-, tri-, and so on, are used to indicate multiple, identical substituents. H3C CH2 CH CH2 CH3 CH2 CH3 1 2 3 4 5 6 Correct numbering 6 5 4 3 2 1 Incorrect numbering R- group -CnH2n+1 e.g. –C6H13 hexyl Naming Alkanes: Nomenclature 10 — although carbon atoms in these cyclic alkanes remain sp3 hybridized the rather small bond angles in most result in strained and weak C-C bonds. more reactive than normal alkanes. — names CH3 CH2CH3 CH2CH2CH3 CH CH3H3C CH3 4 1 3 2 1 2 345 6 methylcyclopropane 1-ethyl-2-propylcyclobutane 1-isopropyl-3-methylcyclohexane 22.2 Alkenes and Alkynes Alkenes • Hydrocarbons containing at least one C=C bond • general formula: CnH2n C C H H H H ethene (ethylene) sp2 hybridized carbons Figure 22.7: Bonding in ethylene 11 Figure 22.8: Bonding in ethane • Naming alkenes root name + -ene suffix (compare root name + -ane suffix in alkanes) → CH2=CH2 ethene (common name: ethylene) 1 2 3 4 1 2 3 4 → CH2=CHCH2CH3 CH3CH=CHCH3 1-butene 2-butene location of double bond indicated by the lowest-numbered carbon atom involved in the bond. • Cis-trans isomerism in alkenes C C H3C H H CH3 C C H3C H CH3 H trans-2-butene cis-2-butene geometric and stereoisomers — consequence of the restricted rotation around the C=C double bond . 12 Alkynes • Hydrocarbons containing at least one C≡C bond • general formula: CnH2n-2 • Naming of alkynes – Root name + -yne suffix • Examples C2H2 H-C≡C-H ethyne (common name: acetylene) HC C CHCH2CH3 CH3 C CHC CH3 CH3 H3C H3C C C CH2CH2CH3 1 2 3 4 5 12 34 1 2 3 4 5 6 cyclohexene 4-methyl-cyclopentene cyclohexyne CH3 1 2 3 4 highly strained and unstable 3-Methyl-1-pentyne 3,3-Dimethyl-1-butyne 2-Hexyne • The triple bond and π bonds in alkynes (see Figure 22.10) Cyclic alkenes and alkynes Figure 22.10: Bonding in acetylene