Organic Chemistry Week 1 Notes
Organic Chemistry Week 1 Notes CHEM 2451
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This 0 page Class Notes was uploaded by Shea Claflin on Saturday January 9, 2016. The Class Notes belongs to CHEM 2451 at University of Denver taught by Dr. Peter J. Harrington in Fall 2016. Since its upload, it has received 155 views. For similar materials see Organic Chemistry I in Chemistry at University of Denver.
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Date Created: 01/09/16
Organic Chemistry Dr Peter Harrington Notes Week 1 14 Carbon essential element of ochem Isotopes of Carbon Carbon12 most abundant 989 Carbon13 has one extra neutron 11 of protons and neutrons gt 13 C of protons gt 6 0 Focus on the electrons they are distributed in the space around the nucleus Aufbau Principlequot also can be thought of as the building upquot principle Spherical shells 1 2 3 4 Orbitals s p d f Orbitals area in space where an electron is likely to be found Pauli Exclusion Principle each orbital can contain only 2 electrons and they must be paired with opposite spin Hund s Rule when lling orbitals with the same energy each orbital gets 1 electron before any get 2 like putting houses on a monopoly board Valence shell shell farthest from nucleus highest in energy that contains electrons Valence electrons electrons located in the valence shell Example of electron con guration Ne 1522522p6 Octet Rule elements want to ll their valence shells with 8 electrons Example of ionic compound in which electrons completely transfer from one atom to another LiF Lithium Fluoride 16 Electronegativity ability of an atom in a molecule to attract shared electrons to itself Ranges from 0 low t e39 For NaCl an ionic bond iguration Electronegativity 93 11Na lsv a 1522522p6 Electronegativity 316 17C ls 22522p63sz3p5 A 223 These new con gurations satisfy the c HH or H2 dihydrogen or hydrogen gas It doesn t make sense to transfer an electron Trom one H to tne other because they have the same electronegativity 1H 15392 H H H or electron con guration 39 H H 1H 152 H like 2He H2 satis es the duet rule for hydrogen It is much more common in ochem for atoms to share electrons in covalent bonds I39ll H C H A CH4 methane gt 90 of natural gas Electronegativity 255 6C 1522522cy2 C Electronegativity 270 1H ls2 39 39 H A 035 O O Clz molecular chlorine or chlorine gas quot 17C 1522522p63sz3p5 Cl 39 39 Cl Cl 0 NH3 ammonia gas at room temperature 25 C boiling point 33 C 2 2 3 HNH 7N ls 25 2p I 1H 152 H C2H4 ethylene minor component of natural gas C2H2 acetylene Bonds get stronger as bond order increases single doubfeC lfpfel Assigning Charges Formal charge FC the positive or negative charge an atom owns in a molecule Formal charge of valence electrons in isolated atom of electrons the atom owns in the molecule or Formal charge of valence electrons nonbonding electrons 12 bonding electrons H20 FCoxygen 6 O HI5H FChydrogen 1 O quot H30 Hydronium FCoxygen 6 2 123 HLEQHW FChydrogen 1 122 H OH39 Hydroxide FCoxygen 6 6 122 FChydrogen 1 122 We can avoid doing calculations by just counting the number of bonds an atom has The following atoms have a formal charge of 0 when they have the following number of bonds 1 4 3 2 1 H C N O F Cl Br With still bigger molecules your rst connectivity option should have the least electronegative elemnt in the middle of the molecule When drawing C02 carbon would be place in the middle 18 C02 carbon dioxide NCS39 Na sodium thiocyanate 1 Connect the atoms 2 Add one electron the anion to N or S 3 Use more doubletriple bonds to satisfy octet rue 4 Electron bookkeeping 1 N 5 1 C 4 1 S 6 Anion 1 Total e 16 electrons Both are correct dot structures together they represent the resonance hybrid for the thiocyanate atom The charge is spread out over 2 atoms it is deocaized Note is not the same as a l TOWS N339 Na sodium azide electrons 1 Connect atoms 2 Add 1 electron anion 3 Make doubletriple bonds 4 Don t forget formal charges Azide anion equilibrium x 31anion 16 C3H6 acetone nail polish remover Electron bookkeeping 3 C 12 O 6 H 6 H H H 19 6 C Anion 1 Total e 24 I I electrons H H 18 electrons present with give structure look for atoms without octet satis ed when placing remaining electrons we could put all 6 electrons on but C would not have a full octet We could put 2 on C but then 0 would not be satis ed There is a double bond between 0 and C it has no charges so it is the most stable Guidelines for Design of Resonance Structures only nonbonding and doubletriple bonds electrons move don t move atoms especially H s all resonance contributers have the number of electrons and same over all charge Rubric for Grading Importance of Resonance Structures 1 structures with all octets satis ed are more important 2 more covalent bonds more important 3 no positivenegative charge separation more important 4 negative charge on more electronegative atom more important Curved Arrow Notation tracking movement of electrons source to destination can go forward or backward through structures C n O H H H H H H H H H H IL F39I methane ethylene H HH HCH HCCH H Lewis dot structures tell us nothing about geometry Q is H angle 90 degrees s methane planar A NO 1095 degrees NO Tetrahedral Q is HCC or HCH angle 90 degrees s ethane planar A NO 120 degrees YES at Revisit atomic orbital geometry s orbital s is for sphere Sphere surrounds nucleus 90 probability you ll nd the electron in that sphere
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