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| Sequence Rules |
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| Rule 1 |
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| When four different atoms are attached to the chiral carbon, priority depends on atomic number. The atom with the highest atomic number gets top priority. If the two atoms are isotopes of the same element, the atom of higher mass number has higher priority. |
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| Rule 2 |
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| If two atoms attached to the chiral carbon atom are same,
priority cannot be decided according to rule 1. The atoms attached to each of these first atoms need to be compared. For e.g., in sec-butyl chloride |
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| consider the methyl group CH3. The second atoms attached to the methyl carbon are all hydrogen atoms. Now consider the ethyl group C2H5. The second atoms are carbon and hydrogen. Carbon because of its higher atomic number is given higher priority than hydrogen. Therefore the sequence of priority is Cl, C2H5, CH3, H. |
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| Rule 3 |
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| A doubly or triply bonded atom is considered as two or three atoms. For e.g., if we consider an atom Y |
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