1 CHE 102 Chap 19 Chapter 19 Organic Chemistry: Saturated Hydrocarbons

2 CHE 102 Chap 19 Success! First two weeks is key to the 1 st half of the semester Need to build a framework for what we will cover –Naming and Drawing molecules –Physical properties (as a function of structure) –Reactions –Each category above is about 25% of each exam, the last 25% is miscellaneous concepts.

3 CHE 102 Chap 19 Organic Chemistry Study of compounds containing C, H, O, N (other trace elements – P, S, Halogens) Covalent Molecules

4 CHE 102 Chap 19 Lewis Structures (Review Ch 11) # bonds formed by C, H, O, N, Halogens Single, double, triple bonds Molecular geometry

5 CHE 102 Chap 19 Hybridization (Review Ch 10) Lewis Models Fail! Required to explain differences in bond strength and length

6 CHE 102 Chap 19 Hybrid Orbitals s + 3p -> sp 3 Sigma Bonds (  ) = single bonds

7 CHE 102 Chap 19 Representing Organic Molecules Molecular Formula Structural Formula –Lewis structures With electrons With bonds Condensed Formula –Assumes some knowledge of Lewis Structures/Bonding Line Models R-groups

8 CHE 102 Chap 19 Functional Groups Organic compounds with similar structures are grouped into classes as shown in Table The members of each class of compounds contain a characteristic atom or group of atoms called a Functional Group. –is part of a larger molecule. –is composed of an atom or group of atoms that have characteristic chemical behavior. –Chemically, a given functional group behaves in nearly the same way in every molecule it’s part of. MEMORIZE the General Formula’s in Table 19.1

9 CHE 102 Chap 19 Functional Groups

10 CHE 102 Chap 19 Functional Groups

11 CHE 102 Chap 19 Functional Groups

12 CHE 102 Chap 19 IUPAC System for Naming Organic Compounds The method recommended by the International Union of Pure and Applied Chemistry is systematic, generally unambiguous, and internationally accepted. Some trivial or common names are still used.

13 CHE 102 Chap 19 Naming Alkanes 1.Select the longest chain = Main chain –All other chains = side chains 2.Number the carbon atoms in the parent carbon chain from one end to the other, starting at the end closest to the first carbon atom that has a branch chain. 3.Name each branch-chain alkyl group and designate its position on the parent carbon by a number. Multiple side groups use (di, tri, tetra, penta…) Name multiple different groups alphabetically Ties go in alphabetical order

14 CHE 102 Chap 19 Naming the Main Chain

15 CHE 102 Chap 19 Side Group Names Parent name, change –ane to -yl

16 CHE 102 Chap 19 Special Side Groups

17 CHE 102 Chap 19 Don’t Get Confused! The longest chain isn’t always straight The longest chain isn’t always left to right, it can go up/down or curve all around Chain numbers don’t always go left to right Always maximize the number of side chains Ties go in alphabetical order

18 CHE 102 Chap 19 Drawing Alkanes 1.Draw the main chain 2.Number the main chain, attach side chains.

19 CHE 102 Chap 19 Alkyl halides or Haloalkanes Name like regular alkanes Halogen = side chain –F = fluoro –Cl = chloro –Br = bromo –I = iodo The longest chain MUST contain the halogen.

20 CHE 102 Chap 19 Isomers Compounds with: –Same Formula –Different Structure The various individual compounds are called isomers. –e.g. There are two isomers of C 4 H 10.

21 CHE 102 Chap 19 Example of Isomers It is possible to write two structural formulas corresponding to the molecular formula C 4 H 10 :

22 CHE 102 Chap 19 How to Draw Isomers Start with parent compound: –Rip a carbon off, and attach it to the main chain (but not in an end position) –Move carbon along positions in chain Only do ½ the molecule (otherwise its symmetrical/identical) Name molecules to double check you don’t duplicate them –Rip off another carbon and repeat above until you can make no new structures.

23 CHE 102 Chap 19

24 CHE 102 Chap 19 Cycloalkanes

25 CHE 102 Chap 19 Naming Cycloalkanes Main Chain –Just stick “cyclo” in front of it Side Chains –Single group (numbers not needed) –2+ Groups, number clockwise or counter clockwise to give the lowest set of numbers possible

26 CHE 102 Chap 19 Hydrocarbons Contain only C and H –aliphatic (do not contain benzene ring) alkanes, cycloalkanes (Ch 20) alkenes, alkynes –aromatic (contain a benzene ring) Ch 20 –An organic compound is classified as saturated if it contains only single bonds. – An organic compound is classified as unsaturated if the molecules possess one or more multiple carbon-carbon bonds.

27 CHE 102 Chap 19 Physical Properties Alkane molecules are non-polar. –Carbon-carbon bonds are non-polar, since they are between like atoms. –Carbon-hydrogen bonds are only slightly polar. –Low polarity =>low boiling points –Boiling point is a function of mass

28 CHE 102 Chap 19 Physical Properties

29 CHE 102 Chap 19 Reactions Involving Carbon (General) General –Oxidation/Reduction –Substitution –Elimination –Addition Specific to Alkanes –Halogenation –Dehydrogenation –Combustion

30 CHE 102 Chap 19 Recognizing Reactions Examine the products and reactants (classes) –Ex: Alkane + Halogen -> Alkyl Halide –Ex: Alkane + O 2 -> CO 2 + H 2 O + Energy Examine the catalysts or reaction conditions

31 CHE 102 Chap 19 Oxidation When carbon atoms are oxidized, they often form additional bonds to oxygen.

32 CHE 102 Chap 19 Reduction When carbon atoms are reduced, they often form additional bonds to hydrogen.

33 CHE 102 Chap 19 Substitution Reaction If, in a reaction, one atom in a molecule is exchanged by another atom or group of atoms, a substitution reaction has taken place.

34 CHE 102 Chap 19 Elimination Reaction An elimination reaction is a reaction in which a single reactant is split into two products, and one of the products is eliminated. Elimination reactions form multiple bonds.

35 CHE 102 Chap 19 Addition Reaction Two reactants adding together to form a single product is called an addition reaction. An addition reaction can be thought of as the reverse of an elimination.

36 CHE 102 Chap 19 Reactions of Alkanes Combustion Halogenation –a substitution reaction Dehydrogenation –an elimination reaction Cracking –breaking up large molecules to form smaller ones Isomerization –rearrangement of molecular structures

37 CHE 102 Chap 19 Combustion Alkane + O 2  CO 2 + H 2 O + Heat/Energy 2 C 3 H O 2  6 CO H 2 O + Heat/Energy

38 CHE 102 Chap 19 Halogenation CH 3 CH 3 + Cl 2  CH 3 CH 2 Cl + HCl Alkane + X 2 (F, Cl, Br, I)  Alkyl Halide + HX

39 CHE 102 Chap 19 CH 3 CH 2 CH 3  CH 3 CH=CH 2 + H 2 Dehydrogenation Heat Alkane  Alkene + H 2 

40 CHE 102 Chap 19 Isomerization Cracking C 16 H 34  C 8 H 18 + C 8 H 16