CHMY 211 Week 2 Class Notes
CHMY 211 Week 2 Class Notes CHMY 211-001
Popular in Elements of Organic Chemistry
Popular in Organic Chemistry
This 3 page Class Notes was uploaded by Bronwyn on Thursday September 15, 2016. The Class Notes belongs to CHMY 211-001 at Montana State University taught by Kristian H. Schlick in Fall 2016. Since its upload, it has received 52 views. For similar materials see Elements of Organic Chemistry in Organic Chemistry at Montana State University.
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Date Created: 09/15/16
1.3 Molecular Representations, Functional Groups ● Molecular Representations ○ Bond line structure ■ “Carbon at every bend and every end” ■ CH bonds are interpreted ■ Represents geometry ■ Single bonds can rotate ● Conformational Groups ● (Continued from Week 1) 9/5: 1.3 continued 1. 2. ● Functional Groups atom group that shows a characteristic, reactive part of molecules, specific groups have specific reactions, divides compounds into description classes for the entire molecule ■ (R=R group, X=halide) ○ Alkene: double bonded carbons ○ Alkyne: triple bonded carbons ○ Alkyl Halide: halide bonded to an R group ○ Alcohol: ROH ○ Ketone: R=O ○ Aldehyde: HR=O ○ Carboxylic Acid: O=ROH ○ Acyl Halide: O=RX where X is a halide ○ Amide: O=RN ○ Amine: RN ● Formal Charge ○ (e supposed to be there) (e actually there) ○ Charges tell how many CH bonds are in a bond line ● Lone Pair e ○ Drawn to avoid confusion, but often skipped with correct number of bonds ○ Determined by comparing # bonds made to the # of bonds the atom can make ● 3D ○ Normal line = same plane ○ Dashed wedge = into plane ○ Solid wedge = out of plane 9/6 1.4 Resonance, Delocalization ● Resonance ○ Molecules are described better with 2+ structures ○ Curved arrow = redistribution of valence e ○ Contributing structures linked with double headed arrow ○ Molecule is a hybrid of all contributing structures ○ Makes a molecule less stable ○ Leads to a partial charge from e spreading out over several atoms ○ Rules ■ Don’t break single bonds ■ Don’t exceed octet for B, C, N, O, F ■ Include formal charge ■ Overall charge doesn’t change between contributing structures ○ Patterns ■ Allylic = next to double bond ■ Vinylic = at double bond ■ Allylic lone pair = lone pair on allylic atom ■ Allylic positive charge (aka electron hole) = lacking e/bond at allylic atom ■ Lone pair adjacent to positive charge ■ Pi bond to electronegative atom ■ Pi bonds in rings = conjugated bonds ○ Resonance occurs w/ overlapping p orbitals (sp hybrids) 2 ■ Lone pairs adopt sp ● Gains stability ○ Contributor stability ■ Not all structures contribute equally ■ The most stable structure contributes the most ● Formal charge decreases stability with a positive charge on an electronegative atom or a negative charge on a less electronegative atom ● Complete octets increase stability ● C w/ opposite charges decreases stability 9/9 2.1 Acidity, pKa + + ● Acids donate H , bases accept H ○ Many molecules can be both acid or base ● Proton transfer reaction → curved arrow ○ Base <attacks> acid + ■ Base has to take H for acid to lose it ● Strong vs Weak ○ Strong acid/base dissociates completely in water ○ pKa= log(a ) ■ Lower # = more acidic ■ Approximate pKa ● H O = 1.74 3 ● Carboxylic acids = ~4.75 ● Bdiketones = ~9.0 ● Phenols = ~9.9 ● Alcohols = ~16 ● Baldehydes and ketones = ~19.2 ● Alkynes = ~25 ● Amines = ~38 ● Alkenes = ~44 ● Alkanes = ~50 ■ Evaluate equilibrium ● Move to side w/ the weaker acid ● Qualifying Acidity ○ CARDIO ■ Charge = acidity increases w/ + charge ■ Atom = stability increases (acidity decreases) w/ atom size ■ Resonance = increased stability w/ delocalized charge ■ Induction = relative to the electronegative atoms around ■ Orbital = stability decreases with distance (sp greater stability than sp , sp greater stability than sp )
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