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Organic Compounds containing Oxygen, Halogen, or Sulfur Alcohols, Ethers, Alkyl Halides & Thiols • • • • ROH ROR RX RSH • All of these compounds contain a carbon atom that is singly bonded to a heteroatom (other than H or C)! • Alcohols & ethers can be considered organic derivatives of water • Replacing H(s) with one or two alkyl groups • HOH; ROH; ROR Alcohols • Structural Characteristics • R-OH -OH (hydroxyl = functional group) -OH is bonded to a saturated C atom! • Classification • Primary (1˚) • Secondary (2˚) • Tertiary (3˚) C-C-OH C-C-OH | C C | C-C-OH | C Alcohol Nomenclature • IUPAC 1. Name the longest chain (drop the “e” and add “ol” at the end) to which -OH is attached. 2. # the chain from the end nearest the -OH* (# the position of the -OH group). 3. Name/locate any substituents. 4. For rings, -OH is on C#1. IUPAC naming examples l • Ex.: CH3OH Methanol • CH3CH2CH2OH 1-propanol • CH3CHCH3 | OH 2-propanol 3,4-dimethylcyclohexanol • Alcohols with >1 -OH groups • Ex.: CH2CH2 | | OH OH 1,2-ethanediol Alcohol Nomenclature • Common (name “R” as an alkyl group) • Alkyl group name + alcohol • Ex.: CH3OH Methyl alcohol • CH3CHCH3 | Isopropyl alcohol OH • Alcohols with >1 -OH groups • Ex.: Important Common Alcohols • IUPAC • • • • • • Methanol Ethanol 2-propanol 1,2-ethanediol 1,2-propanediol 1,2,3-propanetriol For survival in northern winters, many fish and insects produce large amounts of glycerol that dissolve in their blood, thereby lowering the freezing point. • Common • • • • • • Methyl alcohol Ethyl alcohol Isopropyl alcohol Ethylene glycol Propylene glycol Glycerol (glycerin) How does % relate to “proof”? Constitutional Isomerism • Positional • Ex.: butanol 1-butanol 2-butanol • Skeletal • Ex.: butanol 2-butanol sec-butyl alcohol 2-methyl-2-propanol tert-butyl alcohol Physical Properties of Alcohols • Alcohols have both Polar & Nonpolar character! (-OH) (alkyl) • Properties are determined by which portion dominates • Short chain (<6) - polar end dominates • Long chain (6+) - nonpolar end dominates • BP increases with increasing # of C atoms • Effect of London Dispersion Forces • Water solubility • Short chain - soluble • Long chain - insoluble • Alcohols can Hydrogen bond • • (better with small chain alcohols) affects BP & Solubility in Water • Alkanes cannot Hydrogen bond • (a) The polar hydroxyl functional group dominates the physical properties of methanol. • (b) Conversely, the nonpolar portion of 1- octanol dominates its physical properties. Chemical Reactions of Alcohols • Combustion • CH3OH + O2 --> CO2 + H2O • Two types of Dehydration! • Intramolecular Alcohol dehydration • • • • Conditions: 180˚C and H2SO4 catalyst Result: formation of alkene (elimination/condensation rxn) Ex.: C-C-OH ----> C=C + H2O Ex.: 2-butanol --> • Zaitsev’s rule: major product is alkene w/ greatest # of alkyl groups Chemical Reactions of Alcohols • Intermolecular Alcohol dehydration • Conditions: 140˚C (lower temp!) and H2SO4 catalyst • Result: formation of ether (R-O-R) (condensation rxn) • Ex.: C-OH + HO-C ----> C-O-C + H2O Halogenation Reactions • R-C-OH + X2 ----> R-C-X2 + H2O • Not a particularly common reaction, however Oxidation Reactions • 1˚ alcohol ---> aldehyde ---> carboxylic acid • 2˚ alcohol ---> ketone • 3˚ alcohol ---> No Reaction! The oxidation of ethanol is the basis for the “breathalyzer test.” • Oxidation results in an increase in the number of C-O bonds or a decrease in the number of C-H bonds. Preparation of Alcohols • Alcohols can be prepared in two major ways: • Alkene hydration • Ex.: CH2=CH2 + H2O ----> CH3CH2OH • Addition of H2 to a carbonyl group (-C=O) • Ex.: Aldehyde + H2 ----> 1˚ alcohol Ketone + H2 ----> 2˚ alcohol Phenols • Structural Characteristics • -OH is attached to a C that is part of an aromatic ring. • Ar-OH Nomenclature of Phenols • Phenol = “phenyl” + “alcohol” • IUPAC rules are same as for benzene derivatives. Parent ring is “phenol”. • Ex.: Physical & Chemical Properties of Phenols • Flammable, like alcohols • Phenols cannot be dehydrated. • Oxidation occurs only with strong oxidizing agents. • Halogenation • Weak acids in solution (Ka~10-10) Many commercially baked goods contain the antioxidants BHA and BHT to help prevent spoilage. Occurance & Uses of Phenols • Antiseptics (but phenol derivatives are much safer than phenol itself). • Mouthwashes, Lysol, etc. • Antioxidant - several phenols are preferentially oxidized • Food additives • Vit. E • Flavoring agents • Irritants: poison ivy & poison oak Nutmeg tree fruit. A phenolic compound, isoeugenol, is responsible for the odor associated with nutmeg. Ethers • Structural Characteristics • Functional group = -C-O-C• Remember ascorbic acid? • • • • R-O-R R-O-R’ R-O-Ar Ar-O-Ar Nomenclature of Ethers • IUPAC • Select longest C chain = base name. • Change -yl ending of other group to -oxy. (ie. Methyl becomes methoxy) • Place alkoxy name (w/ locator #) in front of base chain name • Ex.: C-C-O-C-C-C-C • Common • Name the two alkyl groups (alpha order) attached to the O and add the word “ether”. Examples: Isomerism • Consitutional • Partitioning of C atoms (by O) positional! • Isomers of individual alkyl groups • Ex.: C4 ethers • Functional Group Isomers (1st time we encounter this possibility) • Consitutional isomers with different functional groups • Ex.: C3 ether and C3 alcohol Physical & Chemical Properties • Physical • BP = to alkanes; lower than alcohols • No H-bonding w/ self possible • Water soluble • Can H-bond w/ water • NP substances are generally soluble in ethers • Act as anesthetics • Diethyl ether • Chemical • Flammable • React w/ O2 to form unstable (explosive) ccompounds • Unreactive w/ acids and oxidizing agents • Halogenation • Prepared by intermolecular dehydration of 1˚ alcohols Alkyl Halides: Incoming halogen atom (orange sphere) replaces a hydrogen atom in the alkane model. • Naming: • Treat halogen atoms like alkyl groups. • F = fluoro; Cl = chloro; Br = bromo; I = iodo • Ex.: CH3-CHBr-CHBr-CHI-CH2-CH3 Halogenation Reactions General equation: RH + X2 → RX + HX Hydrocarbon + Halogen Halogenated + acid (diatomic) hydrocarbon Ex. CH4 + Cl2 --> CH3Cl + HCl Highly exothermic reaction: can lead to an explosion The process can continue to alter the resulting products as long as the halogen remains in sufficient quantities to drive further reactions. (The halogen would be the __________ reactant.) Space-filling models of the four ethyl halides. Do these molecules act as polar or non-polar? Chlorofluorocarbons (CFCs) • Developed in the 1930's • Very stable compounds composed of C, F, Cl, & H • Freon is the tradename: • Trichlorofluoromethane • Dichlorodifluoromethane Trichloro-trifluoroethane Dichloro-tetrfluoroethane Chloropentafluoroethane Safe, non-toxic, non-flammable alternative to dangerous substances (e.g. ammonia) for aerosol-spray propellants, refrigerants, solvents, and foam-blowing agents CFCs and refrigeration CFCs and propellants UV radiation in the stratosphere The Ozone Layer Chemistry CFCl3 + UV Light ==> CFCl2 + Cl Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 The chlorine free radical atom is then able to attack another ozone molecule Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 and again ... Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 and again... thousands of times! A catalyst! The ozone destruction process requires conditions cold enough (-80oC) for stratospheric clouds to form. Once these stratospheric clouds form the process can take place, even in warmer conditions Ozone consumption has been greatly reduced, however CFCs may linger for another 150 years in the atmosphere 1997 ozone hole 2003 ozone hole Ozone layer thickness Thiols = Mercaptans: sulfhydryl group (-SH) bonded to a saturated C atom • Alcohol - R-OH • C-C-OH (ethanol) • (ethyl alcohol) • Thiol - R-SH • C-C-SH (ethanethiol) • (ethyl mercaptan) Properties of Thiols • Physical • Low BP • No H-bonding • Strong odor • Skunks (3-methyl-1butanethiol) • Methanethiol (additive to natural gas) • Morning breath • Onions (1-propanethiol) • Chemical • Oxidation-Reduction 2 thiols <==> Disulfide • Important in Protein chemistry Thioethers - replace the “O” with “S” (R-S-R) • • • • • • C-S-C C-S-C-C-C Ar-S-C C=C-S-C C=C-C-S-C C=C-C-S-S-C-C=C • Morning Breath = Hydrogen sulfide Methanethiol Dimethyl sulfide… • Onions • Garlic Disulfides are important in some protein structures. What do you need to know? • Structural characteristics (know the functional group) • • • • • • Alcohol Phenol Ether Sulfur Analogs Isomers Nomenclature (the rules for naming the molecules) • Common & IUPAC • Physical properties (basic/simple) • BP; Solubility; Flammability • Occurrence and uses (common) • • Natural (ex.: menthol, skunk, nutmeg, clove, garlic, onion) • Synthetic (ex.: antiseptics, racing fuel, de-icers, antioxidants, anesthetics) Preparation (what basic reactions produce the molecules) • Alcohols - alkene hydration; Phenols - benzene hydration • Ethers - intermolecular alcohol dehydration • Characteristic reactions of the molecules • Combustion; dehydration; halogenation; oxidation