Organic chemistry

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Chapters 10 & 15

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Organic chemistry

  1. 1. CHAPTER 10 & 15 Organic Chemistry Chem 104 Spring K. Dunlap
  2. 2. Organic Chemistry the study of the compounds of carbon. •Organic compounds are made up of carbon and only a few other elements. •chief among these are hydrogen, oxygen, and nitrogen •also present are sulfur, phosphorus, and halogens (fluorine, chlorine, bromine, or iodine)
  3. 3. Why is organic chemistry a separate discipline within chemistry? 1) Historical: scientists at one time believed that a “vital force” present in living organisms was necessary to produce an organic compound. •The experiment of Wö hler in 1828 was the first in a series of experiments that led to the demise of the vital force theory.
  4. 4. 2) The sheer number of organic compounds – Chemists have discovered or made over 10 million organic compounds and an estimated 100,000 new ones are discovered or made each year. – By comparison, chemists have discovered or made an estimated 1.7 million inorganic compounds. – Thus, approximately 85% of all known compounds are organic. 3) The link to biochemistry – Carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds.
  5. 5. Carbon-Carbon Bonds
  6. 6. Models of ALKANES
  7. 7. Predict the shape of methane, CH4 – The Lewis structure shows carbon surrounded by four regions of electron density. – the four regions radiate from carbon at angles of 109.5°, and the shape of the molecule is tetrahedral. – The measured H-C-H bond angles are 109.5°.
  8. 8. MOLECULAR GEOMETRY
  9. 9. Valence-Shell Electron-Pair Repulsion (VSEPR) Model – valence electrons of an atom may be involved in forming bonds or may be unshared. – each combination creates a negatively charged region of electrons around the nucleus. – because like charges repel each other, the various regions of electron density around an atom spread so that each is as far away from the others as possible.
  10. 10. Electron Pair Geometries See Active Figure 8.5
  11. 11. Predict the shape of methane, CH4 – The Lewis structure shows carbon surrounded by four regions of electron density. – According to the VSEPR model, the four regions radiate from carbon at angles of 109.5°, and the shape of the molecule is tetrahedral. – The measured H-C-H bond angles are 109.5°.
  12. 12. Predict the shape of ammonia, NH3 – nitrogen is surrounded by four regions of electron density (3 with single pairs of electrons, and 1 with an unshared pair of electrons). – According to the VSEPR model, the four regions radiate from nitrogen at angles of 109.5°, and the shape of the molecule is pyramidal. – The measured H-N-H bond angles are 107.3°
  13. 13. Predict the shape of water, H2O – The Lewis structure shows oxygen with four regions of electron density (2 regions with single pairs of e-, and 2 with unshared pairs of e-. – According to the VSEPR model, the four regions radiate from oxygen at angles of 109.5°, and the shape of the molecule is bent. – The measured H-O-H bond angle is 104.5°.
  14. 14. Predict the shape of formaldehyde, CH2O – The Lewis structure shows carbon surrounded by 3 regions of electron density; 2 with single pairs of e- and one with 2 pairs of e- forming the double bond to oxygen. – According to the VSEPR model, the three regions radiate from carbon at angles of 120°, and the shape of the molecule is planar (trigonal planar). – The measured H-C-H bond angle is 116.5°.
  15. 15. Predict the shape of ethylene, C2H4 – The Lewis structure shows carbon surrounded by 3 regions of e- density; 2 with single pairs of e- and 1 with two pairs of electrons forming the double bond to the other carbon. – According to the VSEPR model, the three regions radiate from carbon at angles of 120°, and the shape of the molecule is planar (trigonal planar). – The measured H-C-H bond angle is 117.2°.
  16. 16. Predict the shape of acetylene, C2H2 – The Lewis structure shows carbon surrounded by 2 regions of electron density; one region with a single pair of e-, and the other one with three pairs of e- forming the triple bond to carbon. – According to the VSEPR model, the two regions radiate from carbon at an angle of 180°, and the shape of the molecule is linear. – The measured H-C-C bond angle is 180°.
  17. 17. Bond Properties • What is the effect of bonding and structure on molecular properties? Free rotation around C–C single bond No rotation around C=C double bond
  18. 18. Bond Order Double bond = 2nd order Single bond = 1st order Acrylonitrile Triple bond 3rd
  19. 19. Bond Length • Bond length is the distance between the nuclei of two bonded atoms.
  20. 20. Bond Length Bond length depends on bond order. Bond distances measured in Bond distances measured in Angstrom units where 1 A = Angstrom units where 1 A = 10-2 pm. 10-2 pm.
  21. 21. Bond Strength • —measured by the energy required to break a bond. See Table 8.9. BOND enthalpy (kJ/mol) H—H C—C C=C C≡C N≡N Bond dissociation 436 346 602 835 945 The GREATER the number of bonds (bond order) the HIGHER the bond strength and the SHORTER the bond.
  22. 22. What are Functional Groups? • an atom or group of atoms within a molecule that shows a characteristic set of predictable physical and chemical properties. • Functional groups are important because: 1) They undergo the same types of chemical reactions no matter in which molecule they are found. 2) To a large measure they determine the chemical and physical properties of a molecule. 3) They are the units by which we divide organic compounds into families. 4) They provide the basis on which we derive names for organic compounds.
  23. 23. Alcohols contains an OH (hydroxyl) group bonded to a tetrahedral carbon atom. For example, ethanol:
  24. 24. Alcohols may be primary (1°), secondary (2°), or tertiary (3°)
  25. 25. Organic Alcohols
  26. 26. Amines: • a compound containing an amino group. – the amino group may be primary (1°), secondary (2°), or tertiary (3°).
  27. 27. Amines
  28. 28. Aldehydes and Ketones: • Both contain a C=O (carbonyl) group. – Aldehyde: contains a carbonyl group bonded to a hydrogen; in formaldehyde, the simplest aldehyde, the carbonyl group is bonded to two hydrogens.
  29. 29. Ketone: contains a carbonyl group bonded to two carbon atoms.
  30. 30. Aldehydes and Ketones
  31. 31. Carboxylic Acids: • a compound containing a -COOH (carboxyl: carbonyl + hydroxyl) group. carb oxyl – In a condensed structural formula, a carboxyl group may also be written -CO2H.
  32. 32. Carboxylic Acids
  33. 33. Carboxylic ester: ester • a derivative of a carboxylic acid in which the H of the carboxyl group is replaced by a carbon group.
  34. 34. Esters
  35. 35. Chiral Molecules • Is a molecule that has 4 different atoms or groups attached to the carbon •have the same molecular formula, and same order, but differ only in the spatial arrangement • Mirror images No mater how they are rotated they can not be superimposed
  36. 36. In Nature, chiral molecules exist almost exclusively in one form of the other
  37. 37. Chiral molecules have 4 different groups attached to a central atom. A chiral molecule and its nonsuperimposable mirror image are a special kind of isomer called enantiomers. Enantiomers have identical physical properties. The only way we can tell them apart is by seeing their effect on plane polarized light. 10.6
  38. 38. However, the body can tell them apart. These two enantiomers may have very different actions in the human body. One enantiomer fits into a receptor site, while the other does not. The molecule on the right will have (possibly) no affect on the human body. 10.6
  39. 39. The R,S System • Because enantiomers are different compounds, each must have a different name. – Here are the enantiomers of the over-thecounter drug ibuprofen.
  40. 40. The R,S System • The first step is to establish priority. – Priority is based on atomic number. – The higher the atomic number, the higher the priority.
  41. 41. The R,S System • To assign an R or S configuration: 1. Assign a priority from 1 (highest) to 4 (lowest) to each group bonded to the stereocenter. 2. Orient the molecule in space so that the group of lowest priority (4) is directed away from you; the three groups of higher priority (1-3) then project toward you. 3. Read the three groups projecting toward you in order from highest (1) to lowest (3) priority. 4. If reading the groups 1-2-3 is clockwise, the configuration is R; if reading them is counterclockwise, the configuration is S.
  42. 42. Optical Activity – Dextrorotatory: clockwise rotation of the plane of plane-polarized light. – Levorotatory: counterclockwise rotation of the plane of plane-polarized light. Specific rotation: the observed rotation of an optically active substance at a concentration of 1 g/mL in a sample tube 10 cm long.
  43. 43. Consider the two enantiomers above. Dextromethorphan is a safe cough suppressant. Levomethorphan is an addictive opiate. 10.6

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