Cations

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Cations
Carey Sundberg, Part A Chapter 5, "Nucleophilic
Substitution", 263-350 .
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John D. Roberts was born in 1918, starting his
career in 1922. He became Prof. at MIT and then
Prof. at Caltech where he is still active. His
work is centered on mechanisms of organic
reactions.
John D. Roberts graduated from the University of
California at Los Angeles where he had received
A. B. (hons) degree in 1941 and the Ph. D. degree
in 1944. In 1945-1946 he was a National Research
Council Fellow and Instructor at Harvard. Later
on, he went to MIT in 1946 as an Instructor. He
had introduced the terms "nonclassical"
carbocations and "benzyne" into organic
chemistry. He had won numerous awards he is a
member of the National Academy of Sciences (1956)
and the American Philosophical Society (1974). He
received the Welch Award (1990, with W. E.
Doering), the National Medal of Science (1990),
and the ACS Arthur C. Cope Award (1994). Since
1939 his research has been concerned with the
mechanisms of organic reactions and the chemistry
of small-ring compounds. His current work
involves applications of nuclear magnetic
resonance spectroscopy to physical organic
chemistry. Roberts made major research and
pedagogic contributions to mechanistic organic
chemistry. He pioneered the use of 14C and other
isotopic labels to follow molecular
rearrangements as, for example, in the complex
and subtle solvolysis of cyclopropylcarbinyl
systems. He introduced the terms "nonclassical"
carbocations and "benzyne" into organic
chemistry, and used isotopic labeling to
establish the intermediacy of each. Roberts was
early to recognize NMR's potential, and used 1H
NMR to study nitrogen inversion, long-range
spin-spin coupling and conformational isomerism,
and later 13C and 15N NMR to study other
reactions, including the active sites of certain
enzymes. Roberts' superb short books on "Nuclear
Magnetic Resonance" (1959), "Spin-Spin Splitting
in High Resolution NMR" (1961) and "Notes on
Molecular Orbital Calculations" (1961) did much
to popularize and clarify these subjects for
organic chemists. His highly successful text
"Basic Principles of Organic Chemistry" (1964),
written with Marjorie Caserio, introduced
spectroscopy early to undergraduates. Roberts
received many awards, including the Roger Adams
(1967) and Priestley (1987) Medals. An excellent
photographer, Roberts graciously supplied several
of the photographs for the MSU collection.
B.A., 1941, UCLA Ph.D. 1944, UCLA Instructor,
Harvard, 1945-6
One of the joys of being a professor is when an
exceptional student comes along and wants to work
with you. J.D. Roberts,
The Right Place at the Right Time. p. 63.
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Carbocations
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Cationic Systems
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Carbocation Stability
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Carbocation Generation
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Carbocation Stability
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Carbocations
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Preparation of a vinyl cation

• no good nucleophiles
• prevent loss of H
• stabilizing b-Si groups

Müller T., Juhasz, M., Reed, C. A., Angew. Chem.
Int. Ed., 2004, 43, 1543-1546.
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NMR evidence
13C and 29Si NMR chemical shifts

• Only one 29Si signal
• Symmetric in solution (confirms ring closure)
• C is far downfield
• Si resonance is downfield
• No solvent effect

29.1
29.1
75.3

202.4
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IR spectrum
Typical Frequencies CC 1660 cm-1 CC 2200
cm-1 Exp. CC 1987 cm-1 Calculated 1956 cm-1
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Crystal Structure
crystal packing
Müller T., Juhasz, M., Reed, C. A., Angew. Chem.
Int. Ed., 2004, 43, 1543-1546.
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Cyclopropyl Cations
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Carbocations In Bridged Systems
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Carbocation 1,2 Sigmatropic Rearrangements
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Carbocation 1,2 Sigmatropic Rearrangements
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Carbocation 1,2 Sigmatropic Rearrangements
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Carbocation 1,2 Sigmatropic Rearrangements
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The Prins Reaction
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Tandem Prins-Pinacol Reaction
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Overmans Laurenyne Synthesis
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Overmans trans-Kumausyne Synthesis
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Overmans trans-Kumausyne Synthesis
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The b-Silicon Effect
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The b-Silicon Effect
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Reactions of Allylsilanes
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Iminium Ions
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Iminium Ions
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N-Acyliminium Ion Rearrangements
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Aza-Cope Manich Reactions
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Terpenes
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Isoprene Nature's C5 Building Block
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Terpene Biosynthesis
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Terpene Biosynthesis
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Steriod and Squalene Oxide Cyclization
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Steriod Biosynthesis Squalene Oxide Cyclization