Chem241a_Lecture_7

Chem241a_Lecture_7 - Organic Chemistry 241a Prof. Bogdan...

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Or ganic Chemistry 241a Prof. Bogdan Olenyuk Contact Information Office: Old Chemistry 309 olenyuk@email.arizona.edu Phone: (520) 626-0754 Course web site: http://www.chem.arizona.edu/courseweb/074/CHEM241A1_2/FrameSet.html
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Chapter 2: Polar Covalent Bonds: Acids and Bases • Drawing resonance forms • Acids and bases • Noncovalent interactions • Alkanes and their isomers Today we will cover: Reading Assignment: McMurry (the BOOK), Ch. 2.7 – 2.13, 3.1 – 3.2
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Different Atoms in Resonance Forms • Sometimes resonance forms involve different atom types as well as locations • The resulting resonance hybrid has properties associated with both types of contributors • The types may contribute unequally • The “enolate” derived from acetone is a good illustration, with delocalization between carbon and oxygen
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Drawing Resonance Forms • Any three-atom grouping with a multiple bond has two resonance forms
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Example: 2,4-Pentanedione • The anion derived from 2,4-pentanedione – Lone pair of electrons and a formal negative charge on the central carbon atom, next to a C=O bond on the left and on the right – Result: three resonance structures
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Acids and Bases: The Brønsted–Lowry Definition • The terms “ acid ” and “ base ” can have different meanings in different contexts • For that reason, we specify the usage with more complete terminology • The idea that acids are solutions containing a lot of “H + and bases are solutions containing a lot of “OH - ” is not very useful in organic chemistry • Instead, Brønsted–Lowry theory defines acids and bases by their role in reactions that transfer protons (H + ) between donors and acceptors
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Brønsted Acids and Bases •“ Brønsted-Lowry ” is usually shortened to Brønsted •A Brønsted acid is a substance that donates a hydrogen ion (H + ) Brønsted base is a substance that accepts the H + – “proton” is a synonym for H + - loss of an electron from H leaving the bare nucleus - a proton
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Chem241a_Lecture_7 - Organic Chemistry 241a Prof. Bogdan...

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