Prelog rules

Thomson MQW Click Organic Interactive to practice assigning priorities to groups according to the Cahn-lngold-Prelog rules. 

Called the Cnlm-Ingolrf-Prelog rules after the chemists who proposed them, the sequence rules are as follows ... 

Look at the two substituents connected to each double-bond carbon, and determine their priorities using the Cahn-lngold-Prelog rules. Then see whether the two high-priority groups are on the same or opposite sides of the double bond. 

II R has higher priority than R in - A the Cahn-Ingold-Prelog rules... 

Recent examples where the Prelog rule makes the correct prediction are reduction of the cyclohexanedione 33 to give hydroxy ketone 34229, and reduction of the 1,l,1-trihalo-2-alka-nanes 35 and 37 to alcohols 36 and 38 respectively (Rs — CH3, CF3 RL — CC13, see also pp 403, 427, 435 and 446)78. 

The Cahn-Ingold-Prelog rules (1956) are used to designate the configuration of each chiral C in a molecule in terms of the symbols R and S. These symbols come from the Latin, R from rectus (right) and S from sinister (left). Once told that the configuration of a chiral C is R or S, a chemist can write the correct projection or Fischer structural formulas. In our statement of the three rules the numerals 1, 2, 3, and 4 are used some chemists use letters a, b, c. and d in their place. 

If you learned the Cabn-lngold-Prelog rules in organic chemistry, test your recall by Designing the appropriate F.S notation to Ihe molecule shown in Fig. 12.2. Assume lhal the C H< ligand is a single atom" of muss 65 (5 x 13). 

The Cahn-Ingold-Prelog rules work for inorganic compounds too but coordination complexes often have coordination numbers greater then four and may exhibit helical chirality, for example, denoted A and A (or Pand Min the Cahn-Ingold-Prelog system). The formal condition for chirality is that the molecule should not have an improper axis of rotation (i.e. a rotation + reflection axis, 5n =... 

C-13 nmr. 245/f Cahn-Ingold-Prelog rules. 72 Cannizzaro reaction. 312 Caibaldehyde. 303 Carbenes. 32... 

---