Chem 106 Tues 1-25-2011 1) Systematic naming of alkanes 2) Alkenes 3) Alkynes 4) Aromatic compounds (benzene etc) 5) ydrocarbon physical properties 6) Petroleum chemistry 1/25/2011 1
pencil : paper :: paint brush : 1. canvas 42 39 2. painting 3. paint 16 11 4. palette canvas painting paint palette 1/25/2011 2
ydrocarbons Alkanes all sp 3 carbons Cycloalkanes all sp 3 carbons in a ring Alkenes one (or more) C=C bond (sp 2 C) Alkynes one (or more) C C bond (sp C) C n 2n+2 C n 2n (one ring) C n 2n (one C=C) C n 2n-2 (one C C) 1/25/2011 3
Alkane names are based on length of longest chain Need to know C 1 C 10 names. not obvious need to learn if you don t know them 1/25/2011 4
M Systematic names of complex alkanes ( I.U.P.A.C. ) Substituents Parent chain location-numbersubstituentsparent 1/25/2011 5
Substituents are sometimes called radicals. They are molecules but with a atom removed to create an attachment point. methane methyl substituent (C 3 ) ethane ethyl substituent (C 3 C 2 ) 1/25/2011 6
Then substituents can be attached somewhere along a longer chain. 2-methyloctane 1/25/2011 7
Alkane systematic names (1) Find longest chain in molecule C 3 (2) Number the chain starting at end closest to any substituents. (3) Identify the number (di, tri, tetra etc) and type (methyl, ethyl, etc) of substituents. 3 C C C C C C 3 1 2 3 4 5 6 C 3 2,2-dimethylhexane all sp 3 1/25/2011 8
flip 6 3 C C 3 5 4 3 2 1 C C C C C 3 C 3 This is also 2,2-dimethylhexane. It has the same name, therefore it s the same molecule This is an isomer: It has a different NAME and structure. C 3 3 C C C C C C 3 1/25/2011 9 C 3 2,3-dimethylhexane
Structure name Name structure 3,3,4,4,5-pentamethyldecane 1/25/2011 10
Naming an alkane: What is the parent chain of the following compound? 1. hexane 42 2. heptane 17 3. octane 5 0 4. nonane hexane heptane octane nonane 1/25/2011 11
What substituent is not present in the systematic name of the following compound? 1. methyl 2. ethyl 3. propyl 33 17 17 methyl ethyl propyl 1/25/2011 12
Show 2,2,3-trimethylpentane in ACD ChemSketch and yperchem. 1/25/2011 13 Free download at www.acdlabs.com
Cycloalkalkanes have formula C n 2n (one ring) cyclopropane C 2 2 C C 2 cyclohexane cycloheptane Largest known cycloalkane: Cyclodotetracontane (C 42 84 ) 1/25/2011 14
Alkenes contain C=C bond (C n 2n ) C 3 3 C 3 C C 3 1/25/2011 15
Naming alkenes (1) Find longest chain containing BOT CARBONS of C=C. (2) Number the carbons starting at the end nearest C=C. (3) Locate the C=C along the chain using # of FIRST C=. 3 C C 3 1 2 3 4 5 Main chain 5 C s Location of C=C 2-pentene Main chain contains C=C 1/25/2011 16
Some alkenes exist in cis- or trans- geometric isomers C 3 Same atoms or groups compare their positions on C=C. 3 C trans- trans-2-pentene cis- 3 C C 3 cis-2-pentene 1/25/2011 17
No C=C bonds contain π-bond that depends on parallel orientation of the 2 p-orbitals on bonded carbons. This prevents twisting around the bond. Therefore C=C bonds containing different atoms can exist as cis- or trans- isomers C 3 C l C l C l C l C l C l C l C l C 3 cis isomers trans isomers 1/25/2011 18
trans- 4,5- diethyl- 4-nonene 6 7 8 9 C 3 3 C 4 5 C 3 2 3 1 C 3 1/25/2011 19
Alkanes are referred to as saturated hydrocarbons. They have the maximum number of s for a given # of C s. Alkenes are unsaturated - they have fewer s. Unsaturated fats contain C=C bonds along the fatty acid chain. As found in nature, these are usually cis- because the C=C plays a structural role in lipid bilayers. 1/25/2011 20
polar Saturated fatty acid Lard is derived from cell membranes of animals. It is rich in saturated fatty acid components. The straight chains pack tightly into the cell s membrane bilayer. Crosssection through cell membrane as proper structure and function at 37 C. 1/25/2011 21
Plant cell membranes contain unsaturated fatty acids rich in cis-double bonds. These chains are kinked by the cis bond, resulting in disordered lipid bilayer that is more fluid. It remains flexible at low temperatures, which maintains the proper biological functions of the cell membrane. 1/25/2011 22
trans-double bonds in fats are man-made. They are created during partial hydrogenation reactions that adds 2 to C=C bonds using a metal catalyst. The trans-acid packs into membranes in a manner similar to saturated fats. This may be the basis of the unhealthy effects of fats containing lots of trans fatty acids. http://en.wikipedia.org/wiki/trans_fat 1/25/2011 23
Alkynes contain a C C triple bond. Each sp-hybridized carbon contains two unhybridized p-orbitals The four p-orbitals combine to form two π-bonds. C C 1/25/2011 24
-C C- common name is acetylene ( ethyne is the systematic name, but is not used.) 1 2 3 4 C 3 C 2 C C C 2 C 2 C 5 6 7 7-methyl-3-octyne 8 C 3 C 3 Uses: acetylene is welding gas larger alkynes used as synthesis intermediates because the C C bond can be modified in many ways. Some natural molecules such as dynemicin an anticancer drug contain C C bonds. 1/25/2011 25
Alkynes are used in organic synthesis reactions to create specific organic molecules. 2-hexyne cannot be obtained from crude oil or other natural sources. 3 C C C + Base 3 C C C + Base acetylide ion C l 3 C C C C 2 C 2 C 3 3 C C C C 2 C 2 C 3 + Cl 2-hexyne Synthesis products are larger than feedstock hydrocarbons, they have specific structures, and they often have useful chemical or biological properties. 1/25/2011 26
Aromatic hydrocarbons 1/25/2011 27
Aromatic hydrocarbons contain one or more benzene rings. C C C C C C C C C C C C Benzene itself is C 6 6. It is a resonance hybrid of two equivalent forms. This leads to an unusually stable molecule. This is called an aromatic ring which refers to the special stability of 6 π-electrons in a ring of sp 2 -atoms. Sometimes written this way to emphasize bonding symmetry: or 1/25/2011 28
Enhanced stability of the aromatic ring is due to formation of a low-energy π-molecular orbital extending around the ring. 1/25/2011 29
C 3 C 3 C 3 C 3 C 3 C 3 C 3 Toluene (methylbenzene) ortho-xylene meta-xylene para-xylene 1/25/2011 30
Binding energy (kcal/mol)* Toluene (methylbenzene) is 28 kcal/mol more stable than the next-most stable C 7 8 isomer -1530-1540 C 3 3 C C 2 2 C -1550-1560 C 2 C 2 Not aromatic -1570-1580 -1590-1600 -1610 C 3 Toluene * calculated with PM3 semi-empirical method Aromatic There are >100 isomers of C 7 8! 1/25/2011 31
ydrocarbon properties Boiling points vs molar mass GC separation 1/25/2011 32
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igh molecular weight hydrocarbons - strong induced dipoles (van der waals forces) due to their large exposed surface area. 1/25/2011 decane 34
Gas chromatogram of C 1 -C 6 hydrocarbons Courtesy of R. Stolzberg 1/25/2011 35
Courtesy of R. Stolzberg 1/25/2011 36
Courtesy of R. Stolzberg 1/25/2011 37
Distillation Courtesy of R. Stolzberg 1/25/2011 38
Courtesy of R. Stolzberg 1/25/2011 39
Refinery chemistry: Reforming gives lots more gasoline 300-600 oc "catalysts" Crude oil Lots of gasoline 1/25/2011 40
1/25/2011 (from North Pole refinery) Courtesy of R. Stolzberg 41
Courtesy of R. Stolzberg 1/25/2011 42