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Conformation of ethane and n butane
- 2. Ethane
- 3. Conformation of Ethane • When an ethane molecule rotates about it's carbon- carbon single bond two extreme conformations can be result, the staggered and eclipsed conformation. • Here we will use Newman projection to discuss the confirmation. H H H H H H H H H HH H 60° 0° Staggered Eclipsed
- 4. Rotation around bond • If one of the methyl group is allowed to rotate keeping the rest of molecule undisturbed and number of possible arrangement can be obtained.
- 5. 60° 120° 360° 300° 240° 180° H HH H H H HH H H H H H H H HH H H H H H H H H H HH H H H H H H H H H H H H H H (I)- Eclipsed Repulsion more Energy more Less stable (II) - Staggered Repulsion less Energy less More stable (III)-Eclipsed Repulsion more Energy more Less stable (VI)-Staggered Repulsion less Energy less More stable (V)-Eclipsed Repulsion more Energy more Less stable (VII)-Eclipsed Repulsion more Energy more Less stable (IV)-Staggered Repulsion less Energy less More stable
- 6. Energy level • By doing so six possible confirmation can be obtained out of which 3 are staggered (II,IV,VI) and 3 are eclipsed form (I/VII,III,V). • Potential energy of I,III,V,VII is greater than that of II,IV,VI due to repulsive forces. • Stability of II,IV,VI is greater than that of I,III,V,VII. I , III, V, VII > II , IV , VI II, IV, VI > I , III , V , VII
- 8. n-Butane CH3-CH2-CH3 C – C – C – C H H HH HH H H H H 1 432 Kekule structure Skeletal structure condensed structure
- 9. Possible rotation for n-Butane C – C – CH2-CH3 H HH HH 1 2 H3C – C – C – CH3 HH H H 32 Rotation around C1 and C2 Rotation around C2 and C3 Structure I Structure II *
- 10. Conformations of n-Butane • Butane has three carbon-carbon single bond and molecule can rotate about each of them . • If the rotation will be about C2 and C3 bond then confirmation will be symmetrical. • Different conformation of butane can be obtained by rotating about its middle carbon- carbon single bond.
- 11. 60° 120° 360° 300° 240° 180° H3C H3CH3C H3C CH3 CH3 CH3CH3 CH3 H3C CH3 CH3 H3C CH3 H HH H H H H H H H H H HH H H H H H H H H H H H H H H (I)-Fully Eclipsed Very high Repulsion Very high Energy Least stable (II) – Staggered(Gauche) Moderate Repulsion Moderate Energy Moderately stable (III)-Partly Eclipsed Repulsion high Energy high Less stable (IV)-Staggered (Anti) Repulsion less Energy less More stable (VII)-Fully Eclipsed Very high Repulsion Very high Energy Least stable (VI) – Staggered(Gauche) Moderate Repulsion Moderate Energy Moderately stable (V)-Partly Eclipsed Repulsion high Energy high Less stable
- 12. Conformers of n-Butane • Butane has 3 staggered (II,IV,VI) conformer. • IV (Anti conformer), in which the two methyl group are as far apart as possible is more stable and require very less energy. • II , VI (Gauche conformer) • Butane has 3 eclipsed (I/VII,III,V) • I and VII are fully eclipsed • III and V are Partly eclipsed
- 13. Energy level • Potential energy of I,VII is greater followed by III,V and II,VI. Conformer IV require very less energy because bulky group CH3 is far apart. • Stability of IV is greater than that of II,VI followed by III, V and I,VII. I ,VII > III, V > II, VI > IV IV > II, VI > III, V > I, VII
- 15. Conformation for n-Butane C – C – CH2-CH3 H HH HH 1 2 Structure I
- 16. 60° 120° 360° 300° 240° 180° H3C H3C H3C CH2-CH3 CH3 CH3 CH3 H3C-H2C CH3 H HH H H H H H H H H H HH H H H H H H H H H H H H H H CH2-CH3CH2-CH3 CH2-CH3 H3C-H2C H3C-H2C (I)- Eclipsed Repulsion more Energy more Less stable (II) - Staggered Repulsion less Energy less More stable (III)-Eclipsed Repulsion more Energy more Less stable (IV)-Staggered Repulsion less Energy less More stable (VI)-Staggered Repulsion less Energy less More stable (V)-Eclipsed Repulsion more Energy more Less stable (VII)-Eclipsed Repulsion more Energy more Less stable
- 17. Energy level • By doing so six possible confirmation can be obtained out of which 3 are staggered (II,IV,VI) and 3 are eclipsed form (I/VII,III,V). • Potential energy of I,III,V,VII is greater than that of II,IV,VI due to repulsive forces. • Stability of II,IV,VI is greater than that of I,III,V,VII. I , III, V, VII > II , IV , VI II, IV, VI > I , III , V , VII
- 18. Thank you my dear students...!!!