alkanes

Alkanes are organic compounds that consist entirely of single-bonded carbon and hydrogen atoms and lack any other functional groups. Alkanes have the general formula CnH2n+2 and can be subdivided into the following three groups: the linear straight-chain alkanes, branched alkanes, and cycloalkanes.

1. ALKANES Md. Saiful Islam BPharm, MSc North South University Fb Group: Pharmacy Universe

2. Carbon Carbon has four valence electrons; hydrogen has one. • • C • H • • To obtain an octet, carbon forms four bonds . H H • • H  C  H H C H CH 4 , methane • • H H H Review

3. Hydrocarbons Large family of organic compounds Composed of only carbon and hydrogen Saturated hydrocarbons Alkanes Unsaturated hydrocarbons Alkenes, Alkynes & Aromatics C - C C = C C C

4. Methane Tetrahedral Expanded structural formula (Lewis): showing each bond line. CH 4 Molecular formula

5. -The most simple of hydrocarbons species -Entirely composed of single bond and saturated in Hydrogen - Suffixe – ane -General formula: CnH2n+2 (non-cyclic) ALKANES Characteristics:

6. -Same for all alkane structure (following CH4) -Covalent, weakly polar bonds : C, H same electronegativity -Boiling point increase by 20 or 30 degrees for each carbon added (except for very small alkanes , same tendency for M.P but less regular). -C1 to C4: gases, C5-C17: liquid, +C18: solid - Insoluble in water, dilute acids and bases and concentrated H2SO4 Physical properties:

7. Ethane C 2 H 6 Molecular formula Expanded structural formula CH 3 – CH 3 Condensed structural formula: with each carbon atom and its attached hydrogen atoms.

8. Alkanes C n H 2n+2 n: number of carbon atoms

9. Naming of Alkanes C n H 2n+2 Prefix + ane

10. Line-angle Formula CH 3 -CH 2 -CH 2 -CH 2 -CH 3 Propane Butane Pentane CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 3

11. In the IUPAC system: Removing a H from an alkane is called alkyl group. -ane Halogen atoms are named as halo . -ine Naming Substituents -OH Hydroxyl -NO 2 Nitro -yl -O

12. STEP 2 Number the carbon atoms starting from the end nearest a substituent. STEP 3 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain.

13. Give the name of: CH 3  CH 3 ─CH─CH 2 ─CH 3 STEP 1 Longest chain is butane. STEP 2 Number chain. CH 3  CH 3 ─CH─CH 2 ─CH 3 1 2 3 4 STEP 3 Locate substituents and name. 2-Methylbutane

14. Give the name of: CH 3 CH 3   CH 3 ─CH─CH─CH 3 STEP 1 Longest chain is butane. STEP 2 Number chain. CH 3 CH 3   CH 3 ─CH─CH─CH 3 1 2 3 4 STEP 3 Locate substituents and name. 2,3-dimethylbutane

15. STEP 1 Longest chain is pentane. STEP 2 Number chain from end nearest substituent. Cl CH 3   CH 3 ─CH 2 ─CH─CH─CH 3 5 4 3 2 1 STEP 3 Locate substituents and name alphabetically. 3-Chloro-2-methylpentane Cl CH 3   CH 3 ─CH 2 ─CH─CH─CH 3

16. CH 3 CH 3 | | CH 3 ─CH─CH 2 ─CH─CH 3 2,4-dimethylpentane 1 2 3 4 5 Cl CH 3 | | CH 3 ─CH 2 ─CH─CH 2 ─C─CH 2 ─CH 3 | Cl 7 6 5 4 3 2 1 3,5-dichloro-3-methylheptane

17. CH 2 CH 3  CH 3 ─CH─CH 2 ─CH 3 STEP 1 Longest chain has 5 carbon atoms (Pentane). STEP 2 Number chain from end nearest substituent. CH 2 CH 3  CH 3 ─CH─CH 2 ─CH 3 STEP 3 Locate substituent and name. 3-Methylpentane 1 2 3 4 5

18. Constitutional Isomers Have the same molecular formula. Have different atom arrangements (different structural formula). CH 3 CH 2 CH 2 CH 3 Butane CH 3 CHCH 3 2-Methylpropane CH 3 C 4 H 10 C 4 H 10

19. = = = Cyclic Hydrocarbon - Cycloalkane Cyclobutane Cyclopentane Cyclohexane Carbon atoms are joined to form a ring.

20. Naming of Cycloalkanes Prefix “cyclo-” + the name of the open-chain alkane Substituents: One substituent: no location number Two or more substituents: number the ring beginning with the substituent of lower alphabetical order. Chlorocyclohexane 1-Bromo-2-methylcyclohexane 1-Chloro-3-hydroxyl-2-nitrocyclopentane Cl CH 3 Br Cl NO 2 OH 1 1 2 2 3

21. Conformation - 3D shapes Any three-dimensional arrangement of atoms in a molecule that results by rotation about a single bond. The following are three conformations for a butane molecule. 2 3 4 1

22. Conformation - 3D shapes The most stable conformation of a cyclopentane is the envelope conformation . The most stable conformation of a cyclohexane is the chair conformation . All bond angles are approximately 109.5°.

23. In a chair conformation, six C-H bonds are equatorial bonds . six C-H bonds are axial bonds . Conformation - 3D shapes Equatorial Axial

24. The more stable conformation of a substituted cyclohexane ring has the substituent group(s) as equatorial rather than axial. Conformation - 3D shapes H H H H More Stable

25. The same molecular formula and the same connectivity of their atoms, but a different arrangement of their atoms in space . mp & bp of cis < mp & bp of trans Cis & Trans Stereoisomers

26. Cis & Trans Stereoisomers Stereoisomers : Isomers that have the same molecular formulas and the same connectivity of their atoms but a different orientation of their atoms in space.

27. Boiling & melting points of Alkanes Number of carbon atoms ↑ bp & mp ↑ Number of branches ↑ bp & mp ↓ CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 CH 3

28. Preparation of alkanes 1- Hydrogenation of unsaturated hydrocarbon: 2- Hydrolysis of Grignard reagent

29. 3- Reduction of alkyl halides a) by metal and acid or by metal hydrides b) By sodium metal (Coupling reaction) c) By lithium dialkyl cuprate

30. Chemical reactions of Alkanes Low reactivity 1- Combustion: Alkanes react with oxygen. CO 2 , H 2 O, and energy are produced. Alkane + O 2 CO 2 + H 2 O + heat CH 4 + 2O 2 CO 2 + 2H 2 O + energy

31. 2- Halogenation: Alkanes react with Halogens. CH 4 + Cl 2 CH 3 Cl + HCl Heat or light Chemical reactions of Alkanes Low reactivity CH 3 Cl+ Cl 2 CH 2 Cl 2 + HCl CH 2 Cl 2 + Cl 2 CHCl 3 + HCl CHCl 3 + Cl 2 CCl 4 + HCl Heat or light Heat or light Heat or light Chloromethane Dichloromethane Trichloromethane Tetrachloromethane

32. Natural gas 90 to 95 percent methane. 5 to 10 percent ethane, and a mixture of other low-boiling alkanes, chiefly propane, butane, and 2-methylpropane. Petroleum A thick liquid mixture of thousands of compounds, most of them hydrocarbons, formed from the decomposition of marine plants and animals. Sources of Alkanes