CIP sequence rules

K. Stanley. M. C. Baird,. /. Am. Chem. Soc. 97, 6598 (1975). The authors proposed to use atomic masses which would not be in line with the CIP sequence rules. 

If all the substituents at X or Y are different, the group most preferred according to the CIP sequence rules is selected (examples la, b). 

However, for the reason already outlined (see Section 1,1.8.) some chemists do not like this system and try to avoid it. As the descriptors are based on the CIP sequence rules, which in turn are based on atomic material properties, i.e., the atomic and mass number, the system cannot in general express genetic relationships within a collection of related compounds and throughout the complete range of reactants undergoing a given reaction. Unfortunately, reconciliation of the conflicting demands is impossible. 

Unacceptable Usage in Slereodescription A CTP descriptor is used on the basis of an ad hoc defined preference of ligands, i.e., a preference not in accordance with the CIP sequence rules. 

Applying the pseudo-atom convention to the iron complex in Figure 8, the iodine atom is priority 1, the t1S-C5H3R2 ligand is priority number 2, the phosphorus atom is priority number 3, and carbon is priority number 4.15 When the iron is viewed from the side opposite the priority number 4, the sequence is 1,2,3 in the anticlockwise or 5 direction. The highest priority carbon in the cyclopentadienyl ligand, indicated by an asterisk, is designated with the R chirality symbol by application of the extended CIP sequence rule. 

Paulina Mata, Ana M. Lobo, Chris Marshall, A. Peter Johnson The CIP Sequence Rules Analysis and Proposal for a Revision, Tetrahdron Asymmetry 4, 657-668 (1993)... 

Table 2.1 CIP sequence rule order for commonly encountered groups (the lower the position of a group in the Table, the greater its priority)...

A carbonyl group in ABC=0 is prochiral provided A differs from B the same holds for the faces of both carbons in an alkene R R2C=CR3R4, and for both faces of one carbon in RlR2C=CH3. The upper face of a carbonyl carbon in ABC=0 is given the symbol Re if, after using the CIP sequence rules, the priorities, say, O > A > B decrease clockwise when looking at the face from above . In such a case the opposite face of the carbonyl carbon is Si. 

CIP (Cahn, Ingold, Prelog) method, CIP system The CIP sequencing rules establish the conventional ordering of ligands for the unambiguous description of absolute configuration by descriptors such as R, S P, M E, Z. 

The opposite configuration notation of the product alcohols are due to the CIP sequence rules. The directions of the asymmetric induction are consistent to afford (R)- isomers by si facial addition of hydride for both aliphatic and al-kylaromatic ketones. However, for a-haloketone and a-ketoester, re facial addition of hydride provides (S)-isomeric alcohols. The direct comparison of K-xylide asymmetric reductions reveals that the reagent resembles very closely to that of K-glucoride. 

Cahn-Ingold-Prelog (CIP) sequence rule is used extensively for the assignment of stereochemical descriptors. 

For vicinally disubstituted olefins (and similar double-bond systems) the traditional prefixes cis and trans can be retained, although for all higher substituted systems the descriptors (Z) and ( ) as defined on the basis of the CIP sequence rules must be applied. 

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