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BU CHEM 102 - Bonding Characteristics of Oxygen
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Chem 102 1st Edition Lecture 8 Outline of Last Lecture I. Chapter 13 Lessons 2.10 – 2.16 : Polymerization of Alkenes: Addition Polymers, Alkynes, Aromatic Hydrocarbons ,Names of Aromatic Hydrocarbons, Aromatic Hydrocarbons : Physical properties and sources, Chemical Reactions of Aromatic Hydrocarbons, Fused Ring Aromatic HydrocarbonsOutline of Current Lecture II. Chapter 14: 3.1 - Bonding characteristics of Oxygen Atoms in Organic CompoundsIII. 3.2 - Structural Characteristics of AlcoholsIV. 3.3 - Nomenclature of AlcoholsV. 3.4 - Isomerism for AlcoholsVI. 3.5 - Important Commonly Encountered AlcoholsCurrent Lecture3.1 - Bonding characteristics of Oxygen Atoms in Organic Compounds• Oxygen is a Group VIA Element - Has 6 valance electrons • Two lone pairs • Two bonding pairs, i.e., it can form two covalent bonds • Two single or one double bond • Bonding in organic compounds: – Carbon forms four bonds – Hydrogen forms one bond – Oxygen forms two bonds. 3.2 - Structural Characteristics of Alcohols• Alcohol: An organic compound in which an —OH group is bonded to a saturated carbon atom. • Saturated carbon atom: A carbon atom that is bonded to four other atoms. • General structure: R-OH (OH is functional group) – Examples: CH3OH, C3H7OH – OH in alcohols is not ionic as in NaOH. The Similar Shapes of Water and Methanol• Alcohols may be viewed structurally as alkyl derivatives of water. 3.3 - Nomenclature of AlcoholsCommon Names for Alcohols • Common names for Alcohols (C1-C4 alkyl groups). − Rule 1: Name all of the carbon atoms of the molecule as a single alkyl group. − Example: Methyl (C1), Ethyl (C2), propyl (C3) butyl (C4) − Rule 2: Add the word alcohol, separating the words with a space. IUPAC Rules for Naming Alcohols • Rule 1: Name the longest carbon chain to which the hydroxyl group is attached. The chain name is obtained by dropping the final “-e” from the alkane name and adding the suffix “-ol.” • Rule 2: Number the chain starting at the end nearest the hydroxyl group, and use the appropriate number to indicate the position of the —OH group. (In numbering of the longest carbon chain, the hydroxyl group has precedence over double bonds, triple bonds, as well as over alkyl, cycloalkyl, and halogen substituents.) • Rule 3: Name and locate any other substituents present. • Rule 4: In alcohols where the —OH group is attached to a carbon atom in a ring, the numbering begins with the carbon to which –OH group is attached. The numbering then proceeds in a clockwise or counterclockwise direction to give the next substituent the lower number. The number “1” (for the hydroxyl group) is omitted from the name since by definition the hydroxyl bearing carbon is carbon1. Alcohols with More Than One Hydroxyl Group • Named with slight modification of IUPAC rules. • Alcohol with two hydroxyl groups is named as a diol. • Alcohol with three hydroxyl groups is named as a triol, and so on. • In these names for diols, triols, and so forth, the final -e of the parent alkane name is retained. 3.4 - Isomerism for Alcohols• Constitutional isomerism is possible for alcohols containing three or more carbon atoms. • Two types of isomers– Skeletal isomers – Positional isomers 3.5 Important Commonly Encountered AlcoholsMethyl Alcohol (Methanol) • Good fuel and used as a solvent in paints • Commonly called wood alcohol – original method of its preparation was by heating wood at high temperature in the absence of air. • Currently, nearly all methyl alcohol is produced via the reaction between H2 and CO. • Toxic: oxidized by alcohol dehydrogenase in the body to toxic formaldehyde and formic acid – toxic to the eye and can cause blindness and/or optic nerve damage. – Treated with ethanol: Ethanol stops oxidation of methanol by competing with alcohol dehydrogenase enzyme Ethyl Alcohol (Ethanol) • Also called as drinking alcohol or grain alcohol (obtained by fermentation of grains like corn, rice and barley). • Prepared by fermentation of plant sugars by yeast – Maximum concentration of ethanol: 18% (yeast enzymes are inactivated at higher concentration of alcohol) – Excellent solvent and a fuel Distributed as denatured Alcohol: Toxic substances such as methanol are added to prevent human consumption – Oxidized by body to acetaldehyde – toxic and causes hangover effects of alcohol – Consumption of alcohol during pregnancy can cause birth defects and fetal alcohol syndrome – Also known to cause liver damage, loss of memory and alcoholism (addiction to alcohol) Isopropyl Alcohol (2-Propanol) • Isopropyl alcohol is a three-carbon monohydroxy alcohol. • A 70% isopropyl alcohol in water is marketed as rubbing alcohol (used to combat high body temperature by rubbing on the skin). • Isopropyl alcohol has a bitter taste.• Toxicity: Twice that of ethyl alcohol (often induces vomiting and thus doesn’t stay down long enough tobe fatal). • In the body it is oxidized to acetone. Ethylene Glycol (1,2-Ethanediol) and Propylene Glycol (1,3Propanediol) • A diol with two -OH groups attached on two adjacent carbon atoms. • Colorless, odorless, miscible in water, great antifreeze. • Toxic. • Propylene glycol is nontoxic and is used in drug preparations as solvent. Glycerol (1,2,3-Propanetriol) • Glycerol is a triol with three -OH groups attached on three adjacent carbon atoms. • Clear thick liquid • Byproduct of fat metabolism • Used in skin lotions and soaps • Used in shaving creams due to lubricating properties • Often called biological


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