priority - If A-1 is a higher priority atoms than B-1, then...

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Assigning Group Priorities- The Cahn, Ingold, Prelog rules: 1. Look at the atoms directly attached to each carbon of the double bond. Rank them according to decreasing atomic number. priority of common atoms: I > Br > Cl > S > F > O > N > C > H H 3 C H CH 3 Cl 1 6 6 17 H 3 C H Cl CH 3 1 6 6 17 high priority high priority high priority high priority (E)-2-chloro-2-butene (Z)-2-chloro-2-butene If both high priority atoms are on the same side of the double bond it is designated Z (zusammen= together). If the high priority atoms are on opposite sides of the double bond, it is designated as E (entgegen= across). 2. a. If the two atoms attached to the double bond carbon are identical (designated A and B below), look at all the atoms directly attached to the identical atoms in questions (designated A-1, A-2, A-3 and B-1, B-2, B-3). Assign priorities to all these atoms based on atomic number (1 is the highest priority, 3 the lowest). X A B B-2 A-3 A-1 B-1 A-2 B-3 Group A Group B b. Compare the highest priority atoms, i.e. compare A-1 with B-1.
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Unformatted text preview: If A-1 is a higher priority atoms than B-1, then A is higher priority than B. If A-1 and B-1 are the same atom, then compare the second highest priority atoms directly bonded to A and B (A-2 with B-2); if A-2 is a higher priority atom than B-2, then A is higher priority than B. If A-2 and B-2 are identical atoms, compare A-3 with B-3. c. If a difference still can not be found, move out to the next highest priority group (A-1 and B-1 in the diagram) and repeat the process. H 2 C H 3 C H 3 C H CH 3 6 6 6 1 (Z)-3-methyl-2-pentene high priority high priority examples: C CH 3 CH 3 CH 3 CH CH 3 CH 3 > CH 2 CH 3 > CH 3 > H > CH 2 Cl > CH CH 3 CH 3 O CH 3 > O H 3. Multiple bonds are considered equivalent to the same number of single bonded atoms. C C H = C C H C C C C H H 3 C C CH 2 CH CH 3 = H H 3 C CH 2 CH 3 C C H C C C C C O H = C H O O C H H 3 C CH 2 C O CH 3 H O = H H 3 C CH 2 C O CH 3 H O O C...
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This note was uploaded on 03/11/2012 for the course CHEM 220A taught by Professor Sulikowski during the Fall '08 term at Vanderbilt.

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priority - If A-1 is a higher priority atoms than B-1, then...

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