Chapter 24

1. Chapter 24 Organic Chemistry

2. Overview • Bonding of Carbon • Hydrocarbons • Alkanes and Cycloakanes • Alkenes and Alkynes • Aromatic Hydrocarbons • Naming Hydrocarbons • Derivatives of Hydrocarbons • Organic compounds containing Oxygen • Organic compounds containing Nitrogen

3. Bonding of Carbon • Carbon has 4 valence electrons (2s22p2)  needs 4 electrons to fill octet. • sp3 hydbridization: four bonds to carbon, CH4 • sp2 hydridization: three bonds to carbon; two single bonds and 1 double bond. CH2=CH2 • sp hybridization: two bonds to carbon; 1 single bond and 1 triple bond, CH≡CH • Carbon can bond to other carbon atoms to form very extensive and complicated molecular systems.

4. Hydrocarbons • Compounds containing only carbon and hydrogen • Saturated hydrocarbons contain only single bonds and are sp3 hybridized. (aliphatic) • Unsaturated hydrocarbons contain at least one double or triple bond. (aliphatic) • Aromatic hydrocarbons: very stable unsaturated compounds such as benzene: C6H6. A = propane B = cyclohexane C = acetylene D = benzene

5. Alkanes and Cycloalkanes • Alkanes = acyclic (not cyclic) saturated hydrocarbons • Cycloalkanes = cyclic saturated hydrocarbons. • Molecular formula: gives number and kind of atoms • Structural formula: gives how bonding between different atoms.

6. Alkanes • Often called Paraffins • General formula CnH2n+2 where n = 1 … E.g. n = 1  CH4; n = 2  C2H6, etc. • Straight chain (normal) alkanes = carbon atoms connected to each other to form a chain of carbon atoms:

7. Alkanes: Homologous Series • Homologous series: series of compounds which differ by fixed number of atoms (e.g. for alkanes they differ only by –CH2- group. • The names and physical properties of the first ten alkanes are shown on Fig. 24.1 • Physical properties of homologous series vary in a predictable manner. • MP and BP increase with number of carbons (Molecular Mass).

8. Branched Chain Alkanes; Constitutional Isomers • Branched chain alkanes such as isobutane are hydrocarbons with carbons not always arranged in a straight chain. • Butane and Isobutane have the same molecular formula, but different structure. • Constitutional (Structural) Isomer – compounds with the same molecular formula but different structural formula. Butane and Isobutane (2-methyl propane) are structural Isomers.

9. Cycloalkanes • Hydrocarbons where the carbons form a ring or cyclic structure; General formula: CnH2n.

10. Alkenes and Alkynes • Unsaturated (contains one or more double or triple bonds) hydrocarbons • Double and triple bonds are more reactive than single bonds which makes unsaturated hydrocarbons more reactive than saturated hydrocarbons. • Alkenes (CnH2n) are also called olefins and contain carbon – carbon double bonds. • All atoms around the double bond are in a plane • Molecules containing a double bond can have geometric isomer when there are the same groups on each side of the molecule but they are located in slightly different positions. E.g. 2 - butene exists as cis and trans isomers trans-2-butene cis-2-butene

11. Alkenes: Addition & Oxidation Reactions • Oxidation: Alkenes can be partially oxidized by permanganate to produce a brown precipitate called manganese dioxide: 3C2H5CH=CH2 + 2MnO4(aq) + 4H2O 3C2H5CHOHCH2OH + 2MnO2(s) + 2OH (aq) • Addition: Reactant is added to the two carbons that form the multiple bond: H2C=CH2 + Br2  H2CBrCH2Br • Addition of H2 (called hydrogenation) gives a hydrocarbon H2C=CH2 + H2  CH3CH3 • Unsymmetrical molecules (e.g. HCl, HBr) can add in two ways: Markownikoff’s Rule: addition of unsymmetrical reagent gives product in which the hydrogen adds to the carbon with the most hydrogens attached to it => the second product is the dominant one.

12. Alkynes • Alkynes are compounds containing triple bonds. • Addition reactions of alkynes behave similarly to alkenes (Markownikoff’s rule):

13. Aromatic Hydrocarbons • A cyclic compound containing several degrees of unsaturation (double bonds). • Aromatic compounds have resonance hybrids and thus are more stable than normal unsaturated compounds. E.g. Cl2 does not readily add to an aromatic double bond, but reacts quite rapidly with normal unsaturated compounds.

14. Reactions on Aromatic Rings: Substitution • Aromatic Substitution reaction – Aromatic compound loses a hydrogen atom and another atom or group takes its place. • It is possible for substitution to occur in more than one place on the ring.

15. Naming Alkanes • Straight-Chain Alkanes (see Table 24.1) • Branched chain has substituents on the molecule; does not form a single simple straight chain. • Name branched-chain alkanes using the format: Prefix-Parent-Suffix • Prefix specifies position and number of various substituents • Parent tells how many carbons atoms are present on the longest continuous chain. • Suffix tells to what family the molecule belongs (alkanes: -ane; alkenes: -ene, etc) Branched Chain Alkane

16. 3-methylhexane 3-ethyl-2,3dimethylpentane Naming Alkanes • Determine the longest chain; use the name of that chain as the parent name; be careful to look for the longest chain. • The name of the chain below would be hexane not butane. • Number carbons starting from end nearest substituent. • Name and locate each substituent group (-ane becomes –ylending) • With two or more substituents list them in alphabetical order; use di-, tri- etc. for identical substituents.

17. Functional Groups • Organic compounds often contain elements other than C, H that increase their reactivity. • Functional Groups are the reactive portions of the molecule that undergo predictable reactions depending upon the functional group.

18. List of Organic Functional Groups

19. Names and Properties of the Straight Chain Alkanes Return to Slide 15 Return to Slide 7