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

– 4 single bonds (tetrahedral)– 1 double bond, 2 single bonds (trigonal planar)– 2 double bonds (linear)– 1 triple bond, 1 single bond (linear)

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)

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

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

Name Molecular formula Structural formulaMethane CH4 CH4

Ethane C2H6 CH3CH3

Propane C3H8 CH3CH2CH3

n-Butane C4H10 CH3(CH2)2CH3

Straight-chain alkanes (5 C through 10 C)

• For straight-chain alkanes 5 C through 10 C, use Greek prefix followed by -ane

Name Molecular formula Structural formula

n-pentane C5H12 CH3(CH2)3CH3

n-hexane C6H14 CH3(CH2)4CH3

n-heptane C7H16 CH3(CH2)5CH3

n-octane C8H18 CH3(CH2)6CH3

n-nonane C9H20 CH3(CH2)7CH3

n-decane C10H22 CH3(CH2)8CH3

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)

C CH3H3C

CH3

H

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

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

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!

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)

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

Aromatic hydrocarbons

• Benzene ring: six-membered carbon ring with alternating single- and double-bonds

C

CC

C

CC

H

H

H

H

H

H

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

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

Oxygen-containing functional groups

Alcohol Aldehyde

Ether Ester

Ketone Carboxylic acid

R OH

R O R'

R C

O

R'

R C

O

H

R C

O

O R'

R C

O

OH

• Molecule fragments which symbolize oxygen-containing functional groups

• R and R’: symbols for general hydrocarbon groups

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

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

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)

R C

O

H

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)

R C

O

R'

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)

R C

O

OH

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

CH3CH2 OH HO C

O

CH3 CH3CH2 O C

O

CH3 H2O

Nitrogen-containing functional groups

• Amine: RnNH3-n

• Generally sharp- or strong-smelling

• Ammonia: NH3

• Triethylamine (CH3CH2)3N smells like dead fish

R NH2 RHN R' R N R'

R''

primary(1°)

secondary(2°)

tertiary(3°)

Amides

• Amides: RCONH2 or RCONHR’

• Formed by reaction of amine with carboxylic acid, similar to ester formation

R C

O

NH2 R C

OHN R'