Lecture 1 - Learning Organic Chemistry Memorizing the...

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Unformatted text preview: Learning Organic Chemistry Memorizing the structure, properties, and reactivities of each molecule will severely limit your abilities Organic chemistry is rational and systematic Goal: Learn tools to dissect and analyze organic chemistry that is unfamiliar Pay attention to detail! 1 Study Tips 1. 2. 3. 4. 5. 6. Read the suggested readings before coming to class and record the main ideas. After each lecture, summarize the major ideas and concepts in your notes within 24 hours of class. Annotate these summaries from your study of the textbook Work the problems independently Master the material from each lecture before going to the next one. Spend a few minutes each day on review to prevent becoming overwhelmed on the night before an exam. You cannot for an Organic Syllabus Organic chemistry Structure and reactivity Resonance Acidity and basicity of organic compounds Alkanes Stereochemistry Overview of organic reactions Alkenes Alkynes Alkyl halides Benzene and aromatic compounds Alcohols and phenols Carbonyl compounds Synthesis using the chemistry of 5.12 2 Background Review 1. 2. 3. 4. 5. Atomic Structure Atomic Orbitals Electron Configuration Ionic/Covalent Bonding Lewis Structures 6. Formal Charges 7. Valence Bond Theory 8. VSEPR Theory 9. Hybridization 10. MO Theory Go the the 5.12 Web Page and work through: q Background Handout (PowerPoint and .pdf) q Background Knowledge Quiz Suggested Readings (McMurry): 1.1-1.12, 2.1-2.3 Suggested Problems (McMurry): 1.1-1.16, 1.21-1.47, 2.1-2.9, 2.29-2.35 Lecture 1: Outline q Organic Chemistry q Relationship of Structure, Energy, and Reactivity q Structure q Atoms q Bonding o How/Why Atoms Bond Together o Bonding Patterns q Representing molecules (putting the atoms together) o Lewis and Kekul Structures o Line-angle Formula o 3-D o Orbital Drawings q Functional Groups q Resonance Suggested Readings (McMurry): 2.4-2.12 Suggested Problems (McMurry): 2.36-2.41, 2.43-2.51, 2.53-2.57, 2.59 3 Organic Chemistry What: The study of carbon-containing compounds Why: Pervasive in nature Chemical foundation of biology Improve standard of living (medicines, plastics, pesticides . . .) How: Examine structure and analyze how it governs reactivity What: Carbon-Containing Compounds Middle of second row Li Be B C N O F Can neither accept or give up electrons easily Share e- with other carbon atoms - incredible structure diversity! Hormone CH3 OH O Amino acid H2N DNA base NH2 N Dynamite NO2 H H HO H OH CH3 N N N H O2N CH3 NO2 Estradiol Alanine OCH3 CH3 Adenine TNT OH H N O Capsaicin (peppers) H3C 4 Subtleties in Structure CH3 OH H3C CH3 OH HO O estradiol testosterone H3C O HO H3C O O O H N CH3 O H N CH3 O O H3C O H N CH3 HO HO codeine morphine heroin Why: Life is Based on Organic Compounds 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Universe Crustal Rock Sea Human Other Ar Cl S P Si Al Mg Na Ne F O N C B Be Li He H Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 5 How: Structure and Reactivity Structure - what atoms are present & how they are bonded together Reactivity - potential of structure to undergo chemical change If likely - reactive (unstable) If unlikely - unreactive (stable) Structure Potential Energy Reactivity Potential Energy: - function of position or configuration of components - if low, compound more stable, change less likely - if high, compound less stable, change more likely Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. Structure Foundation of organic chemistry 1. What atoms (besides carbon) are important? 2. How are these atoms bonded together? Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 6 Structure - Atoms of Organic Molecules Food we eat, fragrances we smell, colors we see, clothes we wear 100% 80% 60% 40% 20% Other Cl Ca K S P Mg Na O N C H 0% crude petroleum dry nonvascular plant tissue dry vascular plant tissue dry human muscle tissue Body 23% C (H20 65% mass) Typical drug contains 20-80 atoms (C, H, N, O, F, S, P, Cl, Br, I) Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. Main Atoms in Organic Chemistry H Li Be Na Mg K Ca Sc Ti Rb Sr Y V B Al He C N O F Ne Si P S Cl Ar Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Sn Sb Te I Xe Zr Nb Mo Tc Ru Rh Pd Ag Cd In Electron configuration: number and arrangement of electrons about an atom Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 7 Electron Configuration of Main Atoms Ground State Element Configuration H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar 1s 1 1s 2s 2p 3s 3p 1s2 1s 2s 2 1 1s22s2 1s 2s 2p 2 2 1 1s22s22p2 1s 2s 2p 2 2 3 1s22s22p4 1s 2s 2p 2 2 2 2 2 2 2 2 2 2 2 2 2 2 5 1s 2s 2p6 1s 2s 2p 3s 6 6 6 6 6 1 1s 2s 2p 3s2 1s 2s 2p 3s 3p 2 2 2 1 1s 2s 2p 3s 3p2 1s 2s 2p 3s 3p 3 1s22s22p63s23p4 1s 2s 2p 3s 3p 2 2 6 2 5 1s22s22p63s23p6 Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. Electron Configuration and Valence Electrons Electron redistribution (change in configuration) is the origin of chemical change WHY? Attain lower ENERGY (achieved when outer shell is filled - 8 electrons) Process of chemical bonding: adding or taking away outer shell electrons to gain a closed shell configuration How do atoms maintain 8 electrons as well as participate in chemical bonding? 8 Bonding Possibilities of Main Organic Atoms Each atom has a limited number of possibilities to satisfy octet: 1. Nonbonding (electron pair localized on one atom) 2. Bonding (electron pair shared between two atoms) a. Single bond (1 shared pair) b. Double bond (2 shared pairs) c. H H C N H H H methyl amine Triple bond (3 shared pairs) H H C C O H H O H H C C N H acetonitrile acetic acid (H is exception to octet rule - has 1 electron) Electron Pair Domain - region of high valence shell electron density (bonding or nonbonding) Bonding Patterns: Formal Charge 0 # Electron Pair Domains 4 H 3 2 1 H 0 C C C C C N N N N O O O F F Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 9 Bonding Patterns: Formal Charge +1 # Electron Domains 4 H + 3 2 1 0 H + C + C C N N N N N O + O O O F + F F Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. Bonding Patterns: Formal Charge -1 # Electron Domains 4 H - 3 2 1 H 0 C - C C C N - N N O - O F - F Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 10 Boron B Electron configuration H H B H H Special reactivity H B H H Neutral, but electron deficient can tolerate an incomplete octet better than any other atom in the second row Octet, but charged EN = 2, least suited of all second row elements to carry a negative charge Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. Organic Structures: Summary (so far) Organic Chemistry Relationship of Structure, Energy, and Reactivity q Structure Atoms Bonding How/Why Atoms Bond Together Bonding Patterns q Representing molecules Lewis and Kekule Structures o Line-angle Formula o 3-D o Orbital Drawings q Functional Groups q Resonance Ethanol H H H C C O H H H Lewis Structure H H H C C O H H H Kekul Structure 11 Representing Molecules: Line-Angle Formula H H O H N C C O H H C H H H C H H H H H H H O C C C H I H C C C C O C C H H H H HH H C O H C C H H C C H C H C C H C H C C H H C C H H C H H H Iodomethane Tyrosine Estradiol O H2N OH CH3 OH Line-Angle Formula OH HO Rules of Drawing Line-Angle Formulas Bonds are represented by lines Assume carbon atoms at the ends of lines and where they meet Assume enough C-H bonds to give each carbon atom four bonds (octet) Carbon and hydrogen atoms are only drawn at termini for aesthetics Draw heteroatoms and attached hydrogen atoms (N, O, P, Cl, Br, F, I, etc.) (any atom that is not carbon) H H H H C C C H H O H H OH OH H3C CH3 H O C C H C H C H H H O HO C CH3 H C H C H H Incorrect! (Why?) Don't forget about the implied hydrogen atoms! Always show all lone pairs! (helps with electron bookkeeping) 12 Representing Molecules: 3-D Lewis/Kekul and Line-Angle structures don't tell the whole story! Molecules are not flat - use dashes and wedges to show 3-D image Governed by VSEPR H H C H H H H C H H Line - in plane of paper Dash - going into the paper Wedge - coming out of the paper H H H C C H H H H C HH HH C H H3C H H CH3 H3C H CH3 H Same atoms, different spatial arrangement Representing Molecules: Orbital Drawings I Atomic Orbitals node + + 13 Representing Molecules: Orbital Drawings II sp3 109.5o sp3 Hybrid Orbitals sp3 sp3 sp3 electron density distributed to the corners of a tetrahedron 180o X 120o sp2 electron density distributed to the corners of a triangle (trigonal planar) sp electron density distributed linearly Representing Molecules: Orbital Drawings III Ethylene H C C H H H H C C H Acetylene pi orbital network 14 Functional Groups The atoms of organic molecules exist in common combinations Each combination: unique chemical properties and reactivity behaves similarly in every organic molecule 10 million organic compounds exist! Predict how any one of those compounds reacts by analyzing its "functional groups" groups" Functional Group - group of atoms with characteristic chemical behavior no matter what molecule it's in Chemistry of every organic molecule, regardless of size or complexity, governed by functional groups Functional Groups to Learn Hydrocarbons alkane C C Nitrogen-Containing Oxygen-Containing alcohol C C OH Sulfur-Containing sulfide C S C amine C N nitrile alkene C C C C N thiol C C SH alkyne diene C C OH nitro phenol O C N O N C C C sulfoxide O C S C ether arene imine C O C sulfone O 2+ C S C O O C C S C O epoxide Carboxylic Acid Derivatives carboxylic acid halide O C C X thioester Halogen-Containing alkyl halide C C X ketone O C C C aldehyde O C C H Carboxylic acid anhydride O O C C O C C O C C O C O C C N X aryl halide carboxylic acid O C C OH ester amide 15 On to Resonance . . . Organic Chemistry Relationship of Structure, Energy, and Reactivity q Structure Atoms Bonding How/Why Atoms Bond Together Bonding Patterns Representing molecules Lewis and Kekule Structures Line-angle Formula 3-D Orbital Drawings Functional Groups q Resonance Resonance IF YOU DO NOT UNDERSTAND RESONANCE, YOU WILL NOT PASS 5.12! Resonance is like riding a bike. Once you learn, you never forget . . . 16 When one Lewis structure just isn't enough... Lewis structure for CH3NO2 = 24 valence eResonance contributor H H C N H O O H H C N H O Resonance contributor O H H C N H O d- Resonance Hybrid O d- Electrons are DELOCALIZED A molecule can't always be accurately represented by one Lewis structure These molecules are weighted average, or hybrids, of two or more Lewis structures (electrons do not move to either one of the oxygen atoms or the other) A Resonance Metaphor Figure removed due to copyright reasons. 17 Why is Resonance So Very Important? >95% of the reactions in 5.12 occur because of the attraction of one molecule containing a region of high electron density to a second molecule containing a region of low electron density + To predict how and when two molecules will react, need to be able to predict the regions of low and high electron density O N O O N O O N O Resonance hybrid (lone pairs not depicted in resonance hybrids) dO dN O d- Tracking Changes in e- Configuration O N O O N O O N O Need a way to keep track of the changes in electron configuration between resonance contributors Courtesy of Jeffrey S. Moore, Department of Chemistry, University of Illinois at Urbana-Champaign. Used with permission. Adapted by Kimberly Berkowski. 18 ...
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