Organic Chemistry Reviews Chapter 4

1. Organic Chemistry ReviewsChapter 4 Cindy Boulton September 20, 2009

2. Naming Molecules • Lewis Structure • VSEPR Structure • Bond Line • Molecular Formula • Condensed Formula • Name • Common Name • IUPAC name

3. IUPAC Nomenclature • Formal system of naming organic compounds • “Common” or old names still used • International Union of Pure and Applied Chemistry • Each different compounds should have an unambiguous name • Locants • Prefixes • Parent Compound • Suffixes

4. 1) Locate the longest continuous chain of carbon – Parent Chain • If ring and chain have the same number of carbons, use the ring as the parent chain • If 2 chains have the same number of carbons, use the chain with the more groups attached • 2) Number the longest chain beginning with the end of the chain near the attached group • If same distance to first group on either end, use the numbers that result in the lowest sum • Number the chain end near the group with alphabetical preference • Number the chain end near the group with suffix –ol • 2 ½) Number a ring where • the first group is the first alphabetically (2 groups) • the numbers result in the lowest sum (3 or more groups)

5. 3) Use the numbers to designate the location of the attached group • 4) If 2 or more attached group, each should be numbered • Placed in alphabetic order • Disregard prefixes • 5) If 2 groups are attached to same carbon, use the number twice • 6) If 2 or more groups are identical, indicate by using prefixes: • 2: di-, 3: tri-, 4: tetra-, etc.

6. IUPAC Nomenclature • Unbranched Alkanes • Normal, single bonds • Sp3 hybridized Carbon • CnH2n+2 • All end in –ane • 1: meth-, 2: eth-, 3: prop-, 4: but-, 5: pent-, 6: hex-, 7: hept-, 8: oct-, 9: non-, 10: dec-, 11: undec-, 12: dodec- • Alkyl Groups derived from straight chains • 1: methyl-, 2: ethyl-, 3: propyl-, 4: butyl-, 5: pentyl-, 6: hexyl-, 7: heptyl-, 8: octyl-, 9: nonyl-, 10: decyl-, 11: undecyl-, 12: dodecyl-

7. Constitutional Isomers • Branched Alkanes • Iso- split at the end • Neo- cross shape • Branched Alkyl Groups • Iso- split at end • Neo- cross shape • Sec- attached at secondary carbon • Tert- attached at tertiary carbon

8. Alkyl Halides • Alkanes with a halogen group attached • F: fluoro-, Cl: chloro-, Br: bromo-, I: iodo- • If have a halide and alkyl group attached to Parent Chain • Number with closest group attached to end of chain-no preference • List in alphabetical order • Alkyl Halides • Alkyl group attached to halogen

9. Alcohols • Hydroxyl group attached (-OH) • Suffix –ol indicates alcohol • Number of suffix is on Parent Compound • Numbering of the Parent Chain always begins at end closer to group named as the suffix • An Alcohol give priority to numbering • Parent Chain must have hydroxyl (-OH) group attached directly • Diols • 2 hydroxyl groups attached • Suffix -diol

10. Monocyclic Alkanes • Prefix cyclo- • Groups attached to cycloalkane • If 1 group attached, no need to indicate position • If 2 groups attached, start numbering ring beginning with the group going to be first alphabetically and in direction of the next group having the lowest number possible • If 3 or more groups attached, use numbering that gives the lowest sum possible • CnH2n

11. Identifying Carbons • Carbons identified by the number of Carbons directly attached • Primary (1o): 1 carbon directly attached • Secondary (2o): 2 carbons directly attached • Tertiary (3o): 3 carbons directly attached • Quaternary (4o): 4 carbons directly attached

12. Physical Properties • More branched molecule- lower boiling point and melting point • Reduced molecular surface area • Less energy required to break the molecule apart • More unbranched (linear) molecule- higher boiling point and melting point as molecular weight increases • More molecules can bind because of larger molecular surface • More energy require to break the molecule apart

13. Confirmation Analysis • Newman Projections • View the rotation between two carbon molecules around the sigma bond and the placement of atoms or molecules attached to both carbons • Dihedral Angle or Torsional Angle- Angle of position between two different atoms or molecules connected to different carbons • Staggered Conformation- atoms/molecules attached to the Carbons are directly bisect each other • Dihedral Angle is 60 degrees • Eclipsed Conformation- atoms/molecules attached to the Carbons are directly opposed to one another • Dihedral Angle is 0 degrees

14. Eclipsed vs. Staggered • Most molecules are found in staggered confirmation • Most stable shape • Lowest energy • Less tension • Electron Pairs Repel- want to be at greatest distance apart as possible

15. Potential Energy • Staggered Confirmation- less energy • Anti- Largest group on both carbons are farthest apart (180 degrees) • Gauche- Largest group on both carbons are 60 degrees apart • Eclipsed Confirmation- more energy • Most energy when the largest group on both carbons are directly opposed each other • Torsional Strain- increase energy by being eclipsed confirmation • How much electron pairs are repelling • Eliminate strain by being staggered confirmation

16. Monocyclic Alkanes • Ring Strain = Angle Strain + Torsional Strain • Angle Strain- how much of a deviation from 109.5 degrees- bond angle if Carbon is tetrahedral • Torsional Strain- if eclipsed or staggered • Cyclopropane • Smallest • Angle Strain- about 60 degrees • Torsional Strain- eclipsed • Most strained ring!!! • Cyclobutane • Angle Strain- about 90 degrees • Torsional Strain- eclipsed • Warp along diagonal decreases torsional strain because less eclipsed but angle strain increases to 88 degrees

17. Cyclopentane • Angle Strain- 108 degrees • Torsional Strain- eclipsed • Warp to form an envelop shape • Decrease angle and torsional strain • Cyclohexane • Angle Strain- 120 degrees • Torsional Strain- eclipsed • Warp to from Chair shape • Angle Strain is 109.5 degrees and Torsional Strain is staggered • Ring Strain = 0!!! • Warp to form Boat shape • No Angle Strain but Torsional Strain is eclipsed

18. Axial vs. Equilateral Positions • Axial- hydrogen vertically attached to carbon on the ring • Equilateral- hydrogen horizontally attached to carbon on the ring • Steric Crowding • Crowded in axial positions • Less crowed in equilateral positions • Larger groups prefer to be in equilateral positions • Reduce energy • More stable

19. 13Carbon NMR Spectroscopy • Nuclear Magnetic Resonance • Identifies each unique Carbon in molecule • Uses isotope of Carbon that is not radioactive • Causes the spin of Carbon molecule to be flipped on a magnetic field • Graph • Measure of the Chemical Shift (δ) ppm from 0-200 • A peak for each different type of Carbon • Placement on graph determined by the electronegativity of atoms attached to the Carbon • Size of peak determined by how many Carbons of that type it is representing

20. Chair Conformation of Cyclohexane • Warped 6 member ring • No ring strain: no torsional or angle strain • Axial: • Mountain- bond up • Valley- bond down • Equatorial: bond straight out • Ring Flip Equilibrium • Interconvert axial and equatorial groups attached • Steric crowding in axial positions • Big groups prefer to be in equatorial positions • More stable • Less Gibb’s Free Energy • Difference in Isomer % at Equilibrium and Free-Energy (pg. 161)

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