Structure/Shape of Drugs - Intro to Conformations Flashcards
What is a covalent bond?
When the outer shells of 2 atoms are filled by the sharing of electrons.
What is hybridisation?
Which orbitals are we looking at?
What are the new orbitals after hybridisation?
Mixing orbitals from the second shell to form a new hybrid orbital.
S orbitals mixing with 1, 2 or 3 p orbitals
After hybridisation new orbitals are sp3, sp2 or sp
What is a conformation?
Different possible arrangement of the atoms in space that are interconvertible by rotation around single bonds.
What are the shapes of the different hybridised conformations?
sp3 = tetrahedral (109 degrees) sp2 = planar/trigonal (120 degrees) sp = linear (180 degrees)
What are the most and least stable conformations? i.e. limiting conformations (for ethane and butane)
Bonus point for middle stability for butane.
Eclipsed (ethane) or Syn eclipsed (butane) is the least stable - groups are aligned.
Staggered (ethane) or Anti-staggered (butane - 180 degrees) is the most stable - groups are furthest away from each other.
Gauche staggered is more stable than eclipsed, less than anti-staggered.
Are all conformations the same energy?
Which is lower energy?
Why?
No.
Staggered/anti-staggered is lower energy as it is more stable.
Groups are further apart so less repulsion.
Explain the differing stability of the conformations?
Staggered is the most stable because the groups are positioned furthest apart. This means the least amount of repulsion.
Eclipsed is the least stable because the groups are closest together. Therefore there is greater repulsion.
What is the hybridisation state of cyclohexane?
sp3 tetrahedral
What is the most stable conformation of cyclohexane?
What type of conformation is this?
Describe the structure?
The CHAIR.
It is fully staggered.
Arranged with 6 axial (above/below) and 6 equatorial (parallel to C-C bonds) hydrogen atoms.
What is the less stable conformation of cyclohexane?
The BOAT - higher energy.
Methylcyclohexane can have 2 chair conformations converted via a boat. Are the 2 chairs the same energy?
Which is more stable?
Why?
No they are not the same.
The chair with the methyl group in equatorial position is more stable (parallel to C-C bonds)
In the Axial conformation the methyl clashes with adjacent axial hydrogens (repulsion)
