Isomers

Annotations:

• same molecular formula

1. Constitutional Isomers

   Annotations:

   • Different sequence of bonds
   • Same molecular formula, different atom to atom bonding sequence.
   • The number of constitutional isomers increases sharply with size.
   • Drawing Constitutional Isomers Systematically. The molecular formula can tell us some important informationFor CnH2n+2 the molecule is said to be fully saturated – meaning it only contains single (σ) bonds and no rings. For CnH2n the molecule must contain either one double bond or one ring.
   • The number of rings or π-bonds (called double bond equivalents or DBEs) can be calculated from the molecular formula. Double bond equivalents (DBEs) =½(2n4 + n3 –n1 + 2)Example: C3H6On is number of atoms with subscripted valence n4 = C, n3 = N, n1 = H, halogen n4 = 3 n3 = 0 n1 = 6 DBEs = ½(6 + 0  6 + 2) = 1
   • Remember each DBE must be accounted for by a ring or a π-bond for any structure drawn for that molecular formula.
   • Using the molecular formula and the calculated double bond equivalents (DBEs) the potential functional groups can be determined.
2. Stereoisomers

   Annotations:

   • Different arrangement of groups in space
   1. Conformational Isomers
   2. Configurational Isomers

      Annotations:

      • Interconversion requires breaking bonds
      1. Enantiomers

         Annotations:

         • Non-superimposable mirror images
      2. Diastereomers

         Annotations:

         • Not mirror images