1. TOPIC 1. STRUCTURE AND BONDING (Chapter 1)L1
TOPIC 1. STRUCTURE AND BONDING (Chapter 1)
These packages of notes are designed for use in conjunction with CHEM 2311 lectures. If you miss a lecture, get the completed notes from another student. Reading assignments (from Solomons) are given in the top right corner (S:#-#), along with relevant problems from the end of the chapter.

2. OBJECTIVES
1. Describe distribution of electrons in organic molecules (atomic electronic configurations, Lewis structures)
2. Describe bonding C-C and C-H bonds in organic molecules (hybridization, overlap of atomic orbitals).
3. Describe molecular geometry.

3. ORGANIC CHEMISTRY: YESTERDAY, TODAY AND TOMORROW
Pre-1820: “Vitalism” - belief that “natural compounds” possessed special properties, could not be made by man
1828: Wöhler: preparation of urea (organic) from ammonium cyanate (inorganic)
NH4+OCN CH4N2O
1908: First production of a synthetic plastic, Bakelite
(1930s-50s: Commercialization of commodity plastics:
nylon, polyester, PVC, polyethylene, polypropylene)
1928: Discovery of penicillin (1954: Celphalosporin)
1948: a-helix of protein structure determined (1952: Determination of double helix structure of DNA)
1950s: Oral contraceptives
Recently:
Taxol (anticancer), C60-buckyball, combinatorial drug development...
heat

4. Who Said It…?
“Organic Chemistry nowadays almost drives me mad. To me it appears like a primeval tropical forest full of the most remarkable things; a dreadful endless jungle into which one does not dare to enter for there seems to be no way out”
Frederich Wohler, or You, Spring 2002
                                                              GT

5. Today Major commodities (annual US production) billion lb Ethylene 52
Propylene 28
Dichloroethane 24
Urea 17
Ethybenzene 13
Styrene 11
Ethylene oxide 8
p-Xylene 8
Cumene 7
1,3-Butadiene 4
Acrylonitrile 3
Benzene 2
Aniline 2
Isopropanol 1
o-Xylene 1
2-Ethylhexanol 1
Major US commodity Producers Annual Sales
billion$
DuPont 26
Dow Chemical 18
Exxon 11
General Electric 7
Union Carbide 6
Huntsman 5
ICI Americas 5
Praxair 5
BASF 5
Eastman Chemical 4
BP Amoco 4
Air Products 4
Shell Oil 4
AlliedSignal 4
Ashland Oil 4
Monsanto 4
Celanese 4
Rohm and Haas 4
Major Pharmaceuticals
Prilosec (Astra Pharm Inc., acid reflux)
Lipitor (Parke-Davis, high cholesterol)
Propecia (antibaldness)
AZT (Burroughs Wellcome, HIV)
Prozac (Fluoxetine) (Antidepresent, Lilly)
Viagra (Pfizer)
Zantac (Ranitidine) (Antiulcer, Glaxo)
Claratin (Schering, allergies)
Amoxicillin (Antibiotic; SKB, Squibb)
Acetaminophen Ibuprophen

6. Tomorrow Better food: Better health: Better environment:
Nutrients
Pesticides
Fertilizers
Better health:
Pharmaceuticals
Biomedical engineered implants/replacements
Better environment:
Cleaner processes
Better living….
…through responsible care and stewardship.
Better Living Through Chemistry

7. SOME BASIC STRUCTURAL FEATURES
Empirical Formula
Ratio of atoms in a compound.
Molecular Formula
Number of each atom in a molecule.
Valency
Elements form a fixed number of bonds (H 1, O 2, N 3, C 4).
Structure
Arrangement of atoms and bonds in a molecule.
Isomers
Different compounds with the same molecular formula. Constitutional isomers: Compounds with the same formula, but with different connectivities of atoms.

8. A VERY GOOD PLACE TO START: ELECTRONIC CONFIGURATION OF ATOMS
H 1s1
He 1s2
Li 1s2, 2s1 Be B C N O F Ne

9. BONDING: LEWIS DOT STRUCTURES AND FORMAL CHARGES
S:1.4-7 Prob:
The Octet Rule
Atoms exchange or share electrons to complete the valence shell (adopt Noble gas electronic configuration)
Ionic Bonds
Atoms exchange electrons to form ions which are electrostatically attracted to one another.
Li F Li F He Ne Ar

10. Ionic bonds are typically formed between atoms which are highly electronegative and highly electropositive He Ne Ar

11. Covalent Bonds C H H H H O H H
Atoms share valence shell electrons to form covalent bonds
C H H H H
O H H

12. “Exceptions” to the Octet “Rule”

13. Formal Charge
F = Z – (S/2) – U H B H O H N H C

14. Some Common Valencies
Not:

15. Given the common valencies of atoms (C=4, H=1), there might be a number of possible arrangements. These different structures are called constitutional isomers. Draw all the constitutional isomers with molecular formula C4H10.

16. RESONANCE THEORY
S:1.8 Prob:1.25,29,30
e.g., Carbonate, CO32–: A single Lewis structure does not accurately describe the structure of the carbonate dianion.
Resonance structures: Valid Lewis structures with same connectivity, differing only in the location of electrons. The individual resonance structures do not exist.

18. Overall structure, or “resonance hybrid”, is an average of the resonance structures, and is more stable than any individual resonance structure.
e.g., propenyl cation, C3H5+ e.g., propenyl anion, C3H5-

19. Problem. Draw resonance structures of: (a) nitrate anion, NO3-, and (b) nitronium cation, NO2+. [Make sure that you: do not break the octet rule, show formal charges, and that the net charge on he ion is correct].

20. QUANTUM MECHANICS, ATOMIC ORBITALS AND MOLECULAR ORBITALS
Electrons are contained in atomic orbitals
1s s p
Atomic orbitals overlap to form molecular orbitals

21. E

22. E Filling Orbitals Carbon: maximum of two e– per orbital
Aufbau Principle: e– fill lower energy orbitals
Pauli Principle: e– in same orbitals have different spins
Hund’s rule: degenerate orbitals are filled equally

23. METHANE AND ETHANE: sp3 HYBRIDIZATION
e.g., methane, CH4
hybridization E

24. methane, CH4: gas (bp=-161 °C)
methane, CH4: gas (bp=-161 °C). Used as natural gas, for synthesis of other compounds

25. e.g., ethane, C2H6
ethane, C2H6: gas (bp= -88 °C). Used in manufacture of C2 derivatives; Minor constituent of natural gas.

26. ALKENES: sp2 HYBRIDIZATION
e.g., ethene (ethylene)
hybridization E

27. ethene (ethylene), C2H4: gas (bp= -102 °C)
ethene (ethylene), C2H4: gas (bp= -102 °C). Monomer for preparation of polyethylene, used for synthesis of ethylene oxide.
LDPE
HDPE

28. Alkenes are thermally stable and do not undergo rotation around the C=C bond.

29. Constitutional and Geometric Isomers of Alkenes
Cl2C=CH2 ClCH=CHCl
trans isomer cis isomer
Geometric isomers have the same connectivity of atoms, but different spatial arrangements.
cis trans
bp/oC 4 1
mp/oC

30. ALKYNES: sp HYBRIDIZATION
e.g., ethyne (acetylene)
hybridization E

31. ethyne (acetylene), C2H2: gas (bp= -81 °C)
ethyne (acetylene), C2H2: gas (bp= -81 °C). Used in oxy-acetylene welding torches, for manufacturing of acetic acid.

32. Comparing C-H Bond Lengths in Alkanes, Alkenes and Alkynes
Csp3 + H1s Csp2 + H1s Csp + H1s

33. VALENCE SHELL ELECTRON PAIR REPULSION THEORY
S:1.16 Prob: ,33
VSEPR Theory
Pairs of valence e– (in bonds and lone pairs) repel each other H C H B H H O ::
H . . C . . H
H . . C N : H O H 

34. BOND STRENGTHS Orbital Energy Diagrams E
Strong bonds are formed between atoms with similar size. Longer bonds, and those between two electronegative atoms, are weak.
atomic orbital
Hs; or sp, sp2, sp3
atomic orbital
Hs; or sp, sp2, sp3 E

35. Representative Bond Lengths and Strengths
bond length bond strength
Ǻ kcal/mol kJ/mol
H-H
H-F
H-Cl
H-Br
H-I
H-O
H-C
C-C
C=C
CC
C-O
C=O
C-Cl
C-Br
C-I
Notes:
Conversion to SI units:
1 Ǻ = m = 100 pm
You do not need to know bond strengths!

36. Calculating Heats of Reaction, DH
bonds broken bonds made net change
(energy IN) (energy OUT) O2

37. Problem. Calculate the ΔH for the following reaction.

38. REPRESENTING ORGANIC MOLECULES IN 2D AND 3D
S:1.17 Prob: ,31,32,34
dash condensed bond-line D structure structure structure structure

39. dash condensed bond-line
structure structure structure

40. Problem. What is the molecular formula of each of the following compounds shown as bond-line structures?

41. sp3 carbon atoms are tetrahedral: Practice drawing tetrahedra!

42. Problem. Norethindrone, is a steroidal oral contraceptive
Problem. Norethindrone, is a steroidal oral contraceptive. Identify the hybridization and geometry of each atom, and the length and overlap of atomic orbitals for each bond.

43. SUMMARY: MOLECULAR STRUCTURE CONCEPTS, MODELS, RULES AND THEORIES
Concept Prediction
Octet rule Valency, presence of lone pairs
Lewis Dot Structures Formal charges electronegativity
Electronegativity Polar bonds, molecular dipoles
Bonding Covalent bonds between atoms of similar electronegativity
Ionic bonds between atoms of different electronegativity
VSEPR Molecular geometry
Hybridization Molecular geometry
Resonance Electron distribution

44. TOPIC 1 ON EXAM 1 Types of Questions Preparing for Exam 1
- Identify formal charges, geometry (bond lengths, angles), hybridization.
- Draw and recognize resonance structures, constitutional isomers, atomic and molecular orbitals.
- Do the problems in the book; they are great examples of the types of problems on the exam!
Preparing for Exam 1
- Get up-to-date NOW!
- Work as many problems as possible. Do the problems first, then consult the solutions manual.
- Work in groups, discuss chemistry, teach and test each other.
- Do the “Learning Group Problem” at the end of the chapter.