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Chapter 24: Organic chemistry

Chapter 24: Organic chemistry. Chemistry 1062: Principles of Chemistry II Andy Aspaas, Instructor. Carbon. Carbon: central element of organic chemistry Organic compounds: compounds containing carbon-carbon bonds 4 valence electrons: 4 must be shared from other atoms

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Chapter 24: Organic chemistry

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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: CnH2n+2

  6. Straight-chain alkanes (5 C through 10 C) • For straight-chain alkanes 5 C through 10 C, use Greek prefix followed by -ane

  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 CH3(CH3)CHCH3 (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 (—CH3) • Ethane becomes ethyl as a branch (—CH2CH3), 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 CnH2n • 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 CnH2n just like cycloalkanes • Names end with -ene (compared to -ane ending of alkanes)

  12. Naming alkenes and alkynes • Ethene is the simplest alkene (CH2=CH2) • 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: CH2=CH–CH2–CH3 2-butene: CH3–CH=CH–CH3 • 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 • 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 hydrogenattached • Usually abbreviated –CHO • Methanal: CH2O (common name: formaldehyde) • Ethanal: CH3CHO (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: CH3COCH3 (common name: acetone) • 2-butanone: CH3COCH2CH3 (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 • CH3COOH: ethanoic acid - vinegar (common name: acetic acid) • CH3(CH2)2COOH: butanoic acid - rancid dairy(common name: butyric acid)

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

  23. Nitrogen-containing functional groups • Amine: RnNH3-n • Generally sharp- or strong-smelling • Ammonia: NH3 • Triethylamine (CH3CH2)3N smells like dead fish

  24. Amides • Amides: RCONH2 or RCONHR’ • Formed by reaction of amine with carboxylic acid, similar to ester formation

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