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Chapter 24: Organic chemistry Chemistry 1062: Principles of Chemistry II Andy Aspaas, Instructor.

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1 Chapter 24: Organic chemistry Chemistry 1062: Principles of Chemistry II Andy Aspaas, Instructor

2 Carbon Carbon: central element of organic chemistry –Organic compounds: compounds containing carbon-carbon bonds 4 valence electrons: 4 must be shared from other atoms –4 single bonds (tetrahedral) –1 double bond, 2 single bonds (trigonal planar) –2 double bonds (linear) –1 triple bond, 1 single bond (linear)

3 Hydrocarbons Hydrocarbon: molecule that contains only carbon and hydrogen atoms –Saturated hydrocarbons: only C–C single bonds May be cyclic or acyclic –Unsaturated hydrocarbons: contain some carbon- carbon double and/or triple bonds –Aromatic hydrocarbons: contain benzene rings –(Non-aromatic hydrocarbons are aliphatic)

4 Alkanes and cycloalkanes Alkanes are acyclic saturated hydrocarbons Cycloalkanes are cyclic saturated hydrocarbons Molecular formula: indicates only type and quantity of atoms in a molecule Structural formula: indicates connectivity in the molecule (which atoms are bonded to which) –Structural formulas look like Lewis structures –Condensed structural formulas don’t draw the bonds, but still indicate connectivity

5 Straight-chain alkanes Straight-chain alkanes (or normal alkanes) have all carbons in a row n- at beginning indicates straight-chain (normal) General formula: C n H 2n+2 NameMolecular formulaStructural formula MethaneCH 4 EthaneC2H6C2H6 CH 3 PropaneC3H8C3H8 CH 3 CH 2 CH 3 n-ButaneC 4 H 10 CH 3 (CH 2 ) 2 CH 3

6 Straight-chain alkanes (5 C through 10 C) For straight-chain alkanes 5 C through 10 C, use Greek prefix followed by -ane NameMolecular formulaStructural formula n-pentaneC 5 H 12 CH 3 (CH 2 ) 3 CH 3 n-hexaneC 6 H 14 CH 3 (CH 2 ) 4 CH 3 n-heptaneC 7 H 16 CH 3 (CH 2 ) 5 CH 3 n-octaneC 8 H 18 CH 3 (CH 2 ) 6 CH 3 n-nonaneC 9 H 20 CH 3 (CH 2 ) 7 CH 3 n-decaneC 10 H 22 CH 3 (CH 2 ) 8 CH 3

7 Isomerism in alkanes n-Butane has a contsitutional isomer (same number and kind atoms, different bonds) –Same molecular formula, different structural formula Isobutane: branched, all carbons not in a row CH 3 (CH 3 )CHCH 3 (parentheses mean group is not in the main chain)

8 Branched alkanes More complex branched alkanes require different naming rules –Any of the straight-chain alkanes can be made into “substitutents” - or branches off a main chain –Methane becomes methyl as a branch (—CH 3 ) –Ethane becomes ethyl as a branch (—CH 2 CH 3 ), etc

9 Naming complex branched alkanes Start by identifying the longest carbon chain Identify branches off the longest chain as their substituent name (methyl, ethyl, propyl, etc) Number longest chain starting at end closest to the first branch Name the compound, starting with branches and indicating the number on the main chain to which the branch is attached

10 Cycloalkanes Saturated hydrocarbons which form a ring of carbon atoms General formula C n H 2n Prefix name with cyclo- and name as if straight chain E.g. cyclobutane (4 carbons); cyclohexane (6 carbons) Any organic molecule can be drawn as a line-angle formula, where carbons and hydrogens are not explicitly shown. –Line-angle drawing of cyclohexane is simply a hexagon –Practice drawing!

11 Alkenes and alkynes Alkenes and alkynes: unsaturated hydrocarbons Typically more reactive than alkanes (reactions can occur at carbon-carbon double and triple bonds) –Hydrogenation: addition of two hydrogen atoms across a double bond Alkenes: general formula C n H 2n just like cycloalkanes –Names end with -ene (compared to -ane ending of alkanes)

12 Naming alkenes and alkynes Ethene is the simplest alkene (CH 2 =CH 2 ) –Common name is “ethylene” When there are more than one possible place to put the double bond, it’s location must be indicated –Start numbering carbons at end closest to the double bond, and indicate the lower-numbered carbon involved in double bond –Ex. 1-butene: CH 2 =CH–CH 2 –CH 3 2-butene: CH 3 –CH=CH–CH 3 Alkynes are named the same way, with -yne instead of -ene

13 Aromatic hydrocarbons Benzene ring: six-membered carbon ring with alternating single- and double-bonds

14 Nomenclature of aromatic hydrocarbons For singly substitued benzenes, use substituent names and benzene as the suffix (ex. Methylbenzene, ethylbenzene, etc.) When 2 identical groups are substituted on a benzene, ortho-, meta-, and para- are used to differentiate the isomers Multiple substituents require the benzene ring to be numbered from 1-6 so that the substitutents get the smallest possible numbers

15 Hydrocarbon derivatives Most organic molecules contain elements other than carbon and hydrogen Heteroatom: atom that’s not C or H in an organic molecule Functional group: common grouping of atoms which reacts in a particular way Oxygen-containing functional groups are the most common

16 Oxygen-containing functional groups AlcoholAldehyde EtherEster Ketone Carboxylic acid Molecule fragments which symbolize oxygen- containing functional groups R and R’: symbols for general hydrocarbon groups

17 Alcohols Alcohol: R–OH functional group Named with similar rules to hydrocarbons –Main chain must contain carbon bonded to –OH –Suffix -ol on chain name –Position of –OH group indicated by number (omit if unnecessary) Ex. Methanol, ethanol, 2-propanol

18 Ethers Ether: R–O–R’ Common name: list the two R groups and suffix with “ether” –Ex. Methyl ethyl ether, diethyl ether IUPAC name: alkoxy derivative of longer chain –Ex. Methoxy ethane, ethoxy ethane Diethyl ether (or just ‘ether’) used as solvent, previously an anesthetic

19 Aldehydes Aldehydes, ketones, carboxylic acids, and esters all contain a carbonyl group (C=O double bond) Aldehyde: carbonyl with a hydrogen attached –Usually abbreviated –CHO –Methanal: CH 2 O (common name: formaldehyde) –Ethanal: CH 3 CHO (common name: acetaldehyde)

20 Ketones Ketone: carbonyl with two hydrocarbon groups attached –Abbreviated –CO– –Named with -one suffix on stem name, number indication position of carbonyl Propanone: CH 3 COCH 3 (common name: acetone) 2-butanone: CH 3 COCH 2 CH 3 (common name: methyl ethyl ketone)

21 Carboxylic acids Carboxylic acids contain a carboxyl group, –COOH Named like aldehydes, but with ‘-oic acid’ as suffix Many have common names CH 3 COOH: ethanoic acid - vinegar (common name: acetic acid) CH 3 (CH 2 ) 2 COOH: butanoic acid - rancid dairy (common name: butyric acid)

22 Esters Ester: RCOOR’ Formed by reaction of alcohol with carboxylic acid –Ex. Ethanol + Acetic acid  Ethyl acetate Pleasant, fragrant smells Many familiar fruit smells are esters

23 Nitrogen-containing functional groups Amine: R n NH 3-n Generally sharp- or strong-smelling Ammonia: NH 3 Triethylamine (CH 3 CH 2 ) 3 N smells like dead fish

24 Amides Amides: RCONH 2 or RCONHR’ Formed by reaction of amine with carboxylic acid, similar to ester formation


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