Chapter 23: Organic Chemistry Organic Chemistry is the area of chemistry that focuses on the study of compounds that contain carbon. Organic Compounds are compounds that contain carbon covalently bonded to other atoms. However, compounds like Na2CO3, CO, and CO2 are generally considered to be inorganic molecules. Carbon is a rather unique element in that it can form strong bonds to itself and to other atoms at the same time. Most other elements only form strong bonds with other atoms or with itself (but not both at the same time). This rather unique property of carbon allows carbon to form long chains of carbon atoms that can then have other atoms attached at different points along the chain. Forming long chains of the same type of atom is called catenation.

Isomerism: compounds that have the same chemical formula but are different chemicals. There several types of isomerism: Structural: formulas that are related by having atoms attached in a different order Geometric: formulas that are related by having different orientations of atoms in space that can not be overcome by rotation about a single bond (sometimes called cis/trans isomerism) Optical: formulas that are non-superimposable mirror images of each other (often called enantiomers). As I draw pairs of compounds try to identify each pair by the type of isomerism.

Hydrocarbons: a class of organic molecules that only contain the elements C and H There are four fundamental types of hydrocarbons: Alkanes: general formula CnH(2n+2) (usually called saturated hydrocarbons) Alkenes: general formula CnH(2n) (must contain at least one C=C double bond) Alkynes: general formula CnH(2n-2) (must contain at least one C≡C triple bond) Aromatic: Special class of compounds that have a ring structure and have alternating single and double bonds (see structure of benzene later) where the electrons can become delocalized

Saturated Hydrocarbons (the Alkanes, CnH(2n+2)) The names of alkanes are based on the number of carbon atoms in the formula. We will learn the names of the first 10 alkanes (straight chain). See page 676. Molecular formula Structural Formula Name CH4 CH4 methane C2H6 CH3CH3 ethane C3H8 CH3CH2CH3 propane C4H10 CH3CH2CH2CH3 butane C5H12 CH3CH2CH2CH2CH3 pentane or CH3(CH2)3CH3 C6H14 CH3(CH2)4CH3 hexane C7H16 CH3(CH2)5CH3 heptane C8H18 CH3(CH2)6CH3 octane C9H20 CH3(CH2)7CH3 nonane C10H22 CH3(CH2)8CH3 decane

Drawing/Naming Practice: we will learn to draw alkanes in two different ways.

Structural isomerism: we will learn to draw structural isomers of a given alkane and name them (see naming rules on page 679). Note: a chain that is attached to a parent chain (longest chain) is considered to be a substituent group and is named as an alkyl group (replace the –ane ending of the group with –yl). For example, a two carbon group would be called ethyl.

Molecular formula Structural Formula Name Unsaturated Hydrocarbons (the Alkenes, CnH(2n) and the Alkynes, CnH(2n-2)) The names of alkenes and alkynes are based on the number of carbon atoms in the formula and use the root of the alkane name. Drop the –ane ending from the alkane name and replace it with –ene for alkenes and with –yne for alkynes. If the double or triple bond could be placed in more than one location in the formula, then a number is used to indicate the first atom involved in the multiple bond. Molecular formula Structural Formula Name C2H4 CH2=CH2 ethene C3H6 CH3CH=CH2 propene C4H10 CH3CH2CH=CH2 1-butene C5H12 CH3CH2CH2CH=CH2 1-pentene Etc….. C2H2 HC≡CH ethyne C3H4 CH3C≡CH propyne C4H6 CH3CH2C≡CH 1-butyne C5H8 CH3CH2CH2C≡CH 1-pentyne Etc…...

Drawing/Naming Practice: we will learn to draw alkenes and alkynes in two different ways.

Geometric Isomerism in Alkenes (a, b, and c are groups attached to the carbon atoms in a double bond) C=C a b c The a’s are both on the same side of the double bond in the molecule, therefore we call it “cis”. C=C a b c The a’s are on the opposite sides of the double bond in the molecule, therefore we call it “trans”. C=C a b c Since the two a’s are on one end of the double bond, there can be no cis or trans.

Structural isomerism: we will learn to draw structural isomers of a given alkene or alkyne and name them (see naming rules on page 683 and 686).

Aromatic hydrocarbons: I will draw these by hand in class (see page 687 for the structure of benzene-the most common aromatic compound we will discuss).

Functional Group: any attached group or specific type of bond that gives an organic molecule special reactivity at that location. Alkanes are fairly unreactive (combustion is one of the most common types of reactions of alkanes-this completely destroys all of the structure of the alkane). Any group or specific type of bond that makes the molecule more reactive than the alkane would be considered to be a functional group. The pi bond in a C=C bond is much more reactive than the sigma bond between C-C or C-H, therefore, the C=C is a functional group. The pi bond in a C≡C is similarly a functional group (two pi bonds present). See Figure 3.1 on pages 688-689 for examples of functional groups other than the alkenes, alkynes, and aromatic rings. Examples include: alcohols, alkyl halides, ethers, aldehydes, ketones, amines, carboxylic acids, esters, and amides.

In class we will draw molecules containing various functional groups and give examples of how to name these types of molecules. alcohol, alkyl halide, ether, aldehyde, ketone, amine, carboxylic acid, ester, amide

Reactions of Organic Molecules (some examples) Combustion (reaction with oxygen): usually used to produce energy 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + energy (octane: gasoline) Substitution: one group replaces another CH3CH2CH2Br + KOH → CH3CH2CH2OH + KBr (1-bromopropane) (1-propanol) Addition: two groups add across a double bond CH3CHCH2 + HBr → CH3CHBrCH3 (propene) (2-bromopropane) Condensation: two molecules join together and eliminate water at the same time CH3CO2H + HOCH3 → CH3CO2CH3 + H2O (ethanoic acid) (methanol) (methyl ethnoate) Elimination: a small molecule is eliminated from two adjacent carbon atoms (1-propanol) (propene) CH3CH2CH2OH + acid or base → CH3CHCH2 + H2O

Polymers and Polymerization A polymer is a large molecule made up of repeating small units (called monomers). Polymerization is a reaction where successive monomer units add sequentially to a growing chain. Addition polymers are produced by addition reactions occurring between monomers that contain double bonds. (polyethylene, polypropylene, and polystyrene are examples) Condensation polymers are produced by condensation reactions occurring between monomers that contain two functional groups. (polyethyleneterphthalate (PET) and nylon are examples)