Chapter 25 Hydrocarbons

25.1 Introduction 1. Originally it was though that only living things produced "organic" compounds. Now they can be made in lab. 2. Compounds containing carbon are "carbon compounds". Hydrocarbons contain only hydrogen and carbon

25.1 Hydrocarbon Bonds 1. Methane produced by decaying living things, shows carbon-hydrogen bonding. 2. Alkanes are the simplest hydrocarbons that contain only single covalent bonds. CnH2n+2

3. Methane has 4 valence electrons and forms 4 bonds - CH4 3. Methane has 4 valence electrons and forms 4 bonds - CH4. Methane is a gas at STP and is the simplest alkane.

4. Structural formulas use lines for bonds. - 2 dimensional models.

5. 3 dimensional models are better, and use the VSPER and hybrid orbital theory. Methane is a tetrahedral.

6. Carbon makes stable C-C bonds, which allows for large chains.

7. Ethane C2H6 is simplest alkane with C-C bond.

25.2 Continuous-Chain Alkanes 1. Continuous-chain alkanes contain any number of carbon atoms bonded in a straight chain. 2. Write out carbons and fill with H. Add -ane to end.

3. A group of compounds forms a homologous series if there is a constant increment of change in molecular structure from one compound in the series to the next. Increments of -CH2

4. Propane and butane are homologs of each other. 5. See Table 25.1 for IUPAC system names, page 593. 6. As number of C increases so does boiling and melting point.

7. See Molecular formula, Complete Structural Formula, Condensed Structural formula, page 594.                 

8. Condensed Structural Formulas may leave out bonds or atoms. 9. The names listed in Table 25.1 are recommended by the International Union of Pure and Applied Chemistry (IUPAC).

25.3 Branched-Chain Alkanes 1. Elements other than H may bind to C. Halogens, groups of carbons, oxygen, nitrogen, sulfur, or phosphorus may take place of hydrogen.

2. Substituent is an atom or group of atoms that replace hydrogen. 3.A hydrocarbon substituent is called and alkyl group.

4.  Common groups are CH3- (methyl), CH3CH2-(ethyl), CH3CH2CH2-(propyl). 5. Named by removing ane and add yl.

6. An alkane with one or more alkyl groups is a branched-chain alkane.

7. IUPAC rules for naming: Find longest continuous chain of carbons. Number carbons in main chain in sequence. Start at end with closest substituent. Add numbers to substituents. Use prefixes to indicate group more than once. Di, tri, tetra, penta, etc. List names of alkyl substituents in alphabetical order. (ignore prefixes) Use proper punctuation. Commas separate numbers. Hyphens used to separate numbers and words.

Example: 4-ethyl-2,3-dimethylheptane.

8. Writing structures given names. Find root word and write longest chain. Number the carbons on parent chain. Identify substituent groups and add to proper places. Add hydrogens.

25.4 Properties of alkanes 1. Hydrocarbons are not polar and are not attracted to or mix with water. 2. Force holding molecules together are weak Vander Waals forces. Electrons shared equally in the C-C and C-H bonds. They are gases or low boiling and melting point liquids.

3. "like dissolves like". 2 nonpolar compounds will forma solution. 3a 3. "like dissolves like". 2 nonpolar compounds will forma solution. 3a. Structural isomers are compounds that have the same molecular formula but different structural formulas.

4. Isomers differ in physical properties, boiling points and melting points. Differ also in chemical reactivities. Examples:                                                                                                                                                                                        

25.5 Alkenes and Alkynes 1. Organic comounds containing carbon-carbon double bonds are called alkenes. CnH2n 2. Organic compounds that contain double and triple carbon-carbon bonds are called unsaturated compound

3. They have less than maximum # hydrogens. 4. Alkanes are saturated compounds. 5. Name by finding longest continuous chain that contains double bond (parent alkene). Use ending -ene.

6. Name with double bond closest to beginning. 7. Name substituent groups same. Number alkene bond after naming substituents.

8. Ethene (ethylene) and Propene (propylene) are simplest alkenes 8. Ethene (ethylene)  and Propene (propylene) are simplest alkenes. Examples:                                                                                                                                                                          

9. No rotation occurs around a double or triple bond. 10. 4 hydrogens in ethene are in plane and at 120o. 11. Organic compounds containng carbon-carbon triple bonds are called alkynes. CnH2n-2

12. Ethyne is linear molecule, with hydrogen at 180o. See page 600. 13. Major attractions are still van der Waals forces. Properties do not dramatically change, such as b.p.

25.6 Geometric Isomers - Honors (Lack of rotation is important for isomers.) 1. Trans configuration is when substitued groups are on opposite sides of double bond. 2. Cis configuration is when the substituted groups are on the same side of the double bond.

25.8 Cyclic and Aromatic Hydrocarbons 1. Compounds that contain a hydrocarbon ring are cyclic hydrocarbons. 2. Rings of from 3 to 20 carbons are found in nature. 5 and 6 are most common

3. Aliphatic compounds do not contain rings. 4 3. Aliphatic compounds do not contain rings. 4. Cycloalkanes are named after the parent alkane. See figure 25.16, page 605. 5. A special group of unsaturated cyclic hydrocarbons are known as arenes.

6. Arenes are unsaturated (not maximum hydrogen) cyclic hydrocarbons- contain double bonds. Arenes were originally called aromatic hydrocarbons. Benzene C6H6 is simplest arene.

7. Benzene is 6 carbon ring with one hydrogen on each carbon 7. Benzene is 6 carbon ring with one hydrogen on each carbon. Ring contains 3 double bonds. Bonds show resonance.

8. Resonance occurs when two or more equally valid structures can be drawn for a molecule                                            

9. Molecules with resonance structures are more stable and less reactive than 6 carbon alkanes. 10. Benzene is a flat molecule 11. Structures can be named with benzene as root and substituent on ring.

12. Structures can be named with alkane as root and PHENYL (benzene) as substituent. 13. Depends on length of alkane and number of substituents.

14. Disubstituted benzenes have two substituents 14. Disubstituted benzenes have two substituents. See page 606 for 3 types of dimethylbenzene (ortho-1,2; meta-1,3; para-1,4). Dimethylbenzenes are called xylenes.