Organic Chemistry: Properties and Naming of Alkanes, Alkenes, and Alkynes, Study notes of Chemistry

Download Organic Chemistry: Properties and Naming of Alkanes, Alkenes, and Alkynes and more Study notes Chemistry in PDF only on Docsity! Chapter 22 - Organic Chemistry 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 Carbon is Special 1. Carbon can form strong and short C-C bonds. 2. The C-C bond is short enough to allow sideways overlap of the unused p orbitals, resulting in π bonding. C easily forms carbon- carbon double bonds, and even forms carbon-carbon triple bonds. 3. Carbon has no problem bonding to other elements (H, O, N, S, etc.). Given where C is in the periodic table, it typically forms four bonds, with the notable exception of carbon monoxide. Carbon is Special -- Try Comparing C to Si 1. The C-C bond is much stronger than the Si-Si bond. (Atomic size increases down the group: bonds between atoms become longer and weaker.) 2. BE (C-C) ~ BE (C-O). For Si, BE (Si-O) >> BE (Si-Si). With availability of oxygen in nature, Si will exist mostly with Si-O bonds. 3. Carbon has no d-orbitals to worry about. CH3-CH3 is stable, while SiH3-SiH3 is very susceptible to species with lone pairs of electrons to donate into the vacant d orbitals. Some people spend their whole lives learning about Carbon! Hydrocarbons C + H Compounds containing only carbon and hydrogen with only single bonds and no multiple bonds - Saturated hydrocarbons - Alkanes CnH2n+2 Compounds containing only carbon and hydrogen with only single bonds and no multiple bonds, but a ring structure - Saturated hydrocarbons - Cycloalkanes CnH2n Compounds containing only carbon and hydrogen with double bonds - Unsaturated hydrocarbons - Alkenes CnH2n Compounds containing only carbon and hydrogen with triple bonds - Unsaturated hydrocarbons - Alkynes CnH2n–2 Drawing Alkanes (cont) b) compounds with 5 C atoms and 1 double bond: (5) [C5H10] C=C-C-C-C C=C-C-C C=C-C-C C-C=C-C-C C-C=C-C c) compounds with 5 C atoms and 1 ring: (5) [C5H10] C-C-C-C C C-C-C-C C C C-C-C C C-C-C C-C C-C C C C C CC Rules for Naming Organic Compounds – I 1. Naming the longest chain (root) (a) Find the longest continuous chain of carbon atoms. (b) Select the root that corresponds to the number of carbon atoms in this chain. 2. Naming the compound type (suffix) (a) For alkanes, add the suffix -ane to the chain root. (Several suffixes are listed in table 22.2) (b) If the chain forms a ring, the name is preceded by cyclo-. 3. Naming the branches (prefix) (a) Each branch name consists of a subroot (number of C atoms) and the ending -yl to signify that it is not part of the main chain. (b) Branch names precede the chain name. When two or more branches are present, name them in alphabetical order. Rules for Naming an Organic Compound-II 3. continued: (c) To specify where the branch occurs along the chain, number the main-chain C atoms consecutively, starting at the end closer to a branch, to achieve the lowest numbers for the branches. Precede each branch name with the number of the chain C atom to which that branch is attached. (d) If the compound has no branches, the name consists of the root and suffix. 6 carbons hex- hex- + -ane = hexaneCH3 CH3 CH CH CH2 CH3 CH3 CH2 CH3 methyl ethyl 1 2 3 4 5 ethylmethylhexane 3-ethyl-2-methylhexane 6 Alkenes Alkenes–Carbon compounds that contain at least one C=C double bond. Alkenes have the general formula: CnH2n Alkenes are called unsaturated hydrocarbons The names of alkenes differ from those of alkanes in two respects: 1) The root chain must contain both C atoms of the double bond, even if it is not the longest chain. The chain is numbered from the end closer to the C=C bond, and the position of the bond is indicated by the number of the first C atom in it. 2) The suffix for alkenes is -ene. Examples: H2C=CH2 Ethylene H2C=CH-CH3 Propylene = H2C=CH-CH2-CH3 1-Butene H3C-CH=CH-CH3 2-Butene H3C-CH2-CH=CH2 1-ButenePropene H2C=C-CH3 2-Methyl propene CH3 Alkenes C2H4 Ethylene H2C=CH2 C3H6 Propylene H2C=CH–CH3 C4H8 Butene H2C=CH–CH2–CH3 C5H10 Pentene H2C=CH–CH2–CH2–CH3 C6H12 Hexene H2C=CH–CH2–CH2–CH2–CH3 C7H14 Heptene H2C=CH–( CH2)4–CH3 C8H16 Octene H2C=CH–( CH2)5–CH3 Consider carbon bonded to A, B, C, and D. There are two possible structures. Organic Optical Isomers A D B C A D C B B a nd C d o no t s up er im po se The two structures are mirror images of each other. They are optical isomers of each other. Each of the two forms is asymmetric - no plane of symmetry. An organic molecule is always chiral if it has a carbon atom that is bonded to four different groups. Organic Molecules React in Predictable Ways Functional Groups – atoms or groups of atoms that determine the reactive, structural, or other functional characteristics of a molecule. Understanding Functional Groups is the secret to learning organic chemistry! As the periodic table is to inorganic chemistry, functional groups are to organic chemistry. Four Important Functional Groups C O H Alcohol group (Hydroxyl group) .. .. Ether group C O C.. .. Carboxylic acid group Ester group .. .. C O C O .. .. .. .. C O H O .. .. .... Alcohols CH3OH Methyl alcohol (Methanol) C2H5OH Ethyl alcohol (Ethanol) CH3CH2OH C3H7OH Propyl alcohol (Propanol) H3C CH2 CH2 OH H3C CH OH n-Propyl alcohol CH3 2-Propyl alcoholH3C CH2 CH2 CH2 OH n-Butyl alcohol Ethers Dimethyl ether H3C–O–CH3 Ethyl methyl ether H3C–O–CH2–CH3 Diethyl ether H3C–CH2–O–CH2–CH3 Diphenyl ether C CH CH CH CH C CH CH CH CH CH CH O Esters–II Amyl butyrate C9H18O2–apricot Methyl salicylate C8H8O3–oil of wintergreen Ethyl formate C3H6O2–lemonade n-Octyl acetate C10H20O2–oranges O CH3-CH2-CH2-C-O-CH2-CH2-CH2-CH2-CH3 O H-C-CH2-CH3 O CH3-C-O-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 O C-O-CH3 OH Amines Amines–I NH3 Ammonia CH3NH2 Methyl amine (CH3)2NH Dimethyl amine (CH3)3N Trimethyl amine N CH3 CH3 CH3 N H . .. . CH3 CH3 . . N H H H . . N H H CH3 Structure of a Cationic Detergent Some Molecules with the Amide Functional Group Functional Group Compound Type Suffix or Prefix of name Example Systematic Name (Common Name) alkene -ene ethene (ethelene) alkyne -yne ethyne (acetylene) alcohol -ol methanol (methyl alcohol) ether ether dimethyl ether haloalkane halo- chloromethane (methyl chloride) amine -amine ethylamine C C C C HH HH C C C C HH C O H.. .. Important Functional Groups in Organic Compounds H H C O H H .. .. C O C H H H C O C H H H C X .... .... .. H H C Cl H C N H H H C C N H H H H (see Table 22.4)