Conformational analysis of n butane

This presentation is about the conformation of n-butane.

1. CONFORMATIONAL ANALYSIS OF n-BUTANE SUBMITTED BY MAYUR HARSUKHBHAI MARVANIYA M.Sc CHEMISTRY(SEM-I) 20MSC01014

2. 1.Abstract………………………………………………………………………1 2.Keywords…………………………………………………………………….1 3 .Introduction………………………………………………………………….2 What is stereochemistry?..............................................................................3 What is isomers?...........................................................................................3 What is conformational isomers?..................................................................4 What is conformational analysis…………………………………………..4 4 .Introduction of n-Butane…………………………………………………….5 Preparation of butane…………………………………………………........5 Isomers of butane………………………………………………………..…6 Mass spectrometry of n-Butane………………………………………..…..6 5 .Representation of compound…………………………………………….…..7 Fischer projection…………………………………………………...……...7 Newman projection ……………………………………………..………....8 Sawhorse projection …………………………………...……………….....9 INDEX

3. 6 .Types of strain…………………………………………………………….10 Torsional strain……………………………………………………………10 Steric strain………………………………………………………………..11 Dihedral angle…………………………………………………………….12 7 .Staggered and Eclipsed conformation of n-Butane………………....13 Staggered conformation……………………………………….......13 Eclipsed conformation…………………………………………….14 8 .Conformers of n-Butane…………………………………………..15 Full eclipsed conformer…………………………………………...15 Anti conformer…………………………………………………….15 Gauche conformer………………………………………………………...16 Eclipsed conformer……………………………………………………….16 9 .Conformational analysis……………………..…………………………..… 17 10.Conclusion………………………………………………………………...18

4. The molecule will achieve a different shape, or as the chemists say, it is transformed into a different  conformation . In a real molecule, rotations around these bonds are not fully free. They are subjected to a potential and the molecule adopts during the rotation particular, energetically favorable arrangements.  n -Butane represents the simplest case. The central torsion or dihedral angle determines the relative orientation of the two bonds to the methyl groups to one another. If  n -butane is rotated out of the arrangement with the two bonds to the methyl groups in 180° orientation (trans), the methyl group at the “front” carbon and the hydrogen atom at the “back” carbon will directly coincide which each other at a rotation angle of 120° and 240° called “eclipsed”. In this geometry, they come closer to one another, therefore this arrangement is unfavorable for steric reasons. At a rotation angle of 60° and 300° the groups are again in a staggered geometry, which is an energetically more favorable situation. This arrangement is somewhat less favorable than the staggered  trans  orientation because of the spatial vicinity of the methyl groups, which are now said to be “gauche” to one another. Finally along the rotation path an orientation is adopted at 0° and 360° in which both methyl groups are exactly behind one another. This is an even less favorable orientation. KEYWORDS Conformational, n-Butane, isomers, Torsion, Angle 1 ABSTRACT

5. The different arrangement formed by rotations about a single bond are called conformations, and a specific is called conformer. Pure conformers cannot be isolated in most cases, because the molecules are constantly rotating through all the possible conformations. Butane conformations rotations about the center bond in butane give different molecular shapes. Some conformations can be more stable than others. Butane there will be two different staggered conformations: gauche and anti. The gauche conformation has a dihedral angle of 60° between the methyl groups while the anti conformation has a dihedral angle of 180° between the methyl groups. There distinct eclipsed conformation when the dihedral angle between the methyl groups is 0°, this conformation is referred to as totally eclipsed. When looking at total energy, we see that butane has maxima at 0° and 360° (see graph).  Secondary maxima are found at 120° and 240°and secondary minima are found at 180° (see graph).  This occurs, because the carbon-methane bonds interact differently with other carbon-methane bonds, than they do with carbon-hydrogen bonds.  In addition, the carbon-hydrogen bonds interact differently with other carbon-hydrogen bonds than they do with carbon-methane bonds. So, Here discussion about the conformers of n-Butane and see what type of conformers in Butane. Then we discusses about strain in conformers of n-Butane . 2 INTRODUCTION

6. What is stereochemistry? The part of science with deals with structure in the three dimensions is called stereochemistry. What is isomers? Isomers are non identical compound with the same molecular formula. Types: 1)Structure isomers 2)stereoisomers 3

7. Conformation OR C onformers OR Rotamers Different special arrangements of a molecule that are generated by rotation about single bond that type of isomers is know as conformers OR rotamers. Conformational analysis Conformation analysis is the study of the effect of rotation on the properties of a molecule. 4

8. Butane or  n -butane is an alkane with the formula C 4 H 10 . Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless , easily liquefied gas that quickly vaporizes at room temperature . PREPARATION OF BUTANE 1)WURTZ REACTION CH₃CH₂Br + 2Na + CH₃CH₂Br ⇒ CH₃CH₂CH₂CH₃ + 2NaBr 2)Addition of Hydrogen to alkene in presence of Pt , Pd . CH₃ - CH₂ - CH = CH₂ + H₂ ⇒ CH ₃ - CH₂ - CH₂ -CH₃ 5 INTRODUCTION OF BUTANE

9. Isomers of butane Mass spectrometry of n-Butane: 6

10. 1)FISCHER PROJECTION Fischer projection is 2D structure projection of compound. So Here we represent Fischer projection from wedge dash structure of compound. 7 REPRESENTATION

11. 2)NEWMAN PROJECTION In Newman projection we represent first carbon and last carbon as dot and circle respectively of carbon chain. This projection is helpful when we study of conformers of compound. 8

12. 3) SAWHORSE PROJECTION Sawhorse projection is same as Newman projection. The only different is we see all bonds of compound in sawhorse projection when in Newman projection we only see first and last carbon. 9

13. TORSINOL STRAIN STERIC STRAIN 1) TORSINOL STRAIN : Torsional strain arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation the torsional strain also called eclipsed interaction strain . Torsional strain between eclipsed and staggered ethane is approximately 12.6 kJ (3.0 kcal)/mol. 10 TYPE OF STRAIN IN n-BUTANE

14. 2) Steric strain (nonbonded interaction strain ) Steric strain that arises when atoms separated by four or more bonds are forced closer to each other than their atomic (contact) radii. Fully eclipsed conformers of n-butane is higher energy(5KJ/mole) then other eclipsed conformer because of steric strain. 11

15.  T he angle created by two intersecting planes this angle is know as dihedral angle. 12 DIHEDRAL ANGLE(ɵ)

16. STAGGERED CONFORMATION Drawing butane in possible way, with all carbons in the plane of the page; the line diagram drawn with the carbons zigzagging nicely. 13 Staggered and Eclipsed conformation of n-Butane

17. Here, we’ve chosen to draw out the C-H bonds with all the C-C bonds  eclipsed . Since there is free rotation about all the single bonds, these conformations can interconvert. 14 ECLIPSED CONFORMATION

18. Fully eclipsed conformers Highest energy has methyl groups eclipsed . Steric hindrance  Dihedral angle = 0 degrees 2) Anti conformers Lowest energy has methyl groups anti. Dihedral angle = 180 degrees 15 CONFERMERS OF n-BUTANE

19. 3 )Gauche conformers Methyl closer than in anti conformer Dihedral angle = 60 degrees 4) Eclipsed conformers Methyl groups eclipsed with hydrogen Higher energy than staggered conformer Dihedral angle = 120 degrees 16

20. 17 CONFORMATIONAL ANALYSIS

21. In Conformation analysis of n-Butane we explain steric interactions are what we call repulsions between the electron clouds of substituents that come into close contact, such as in the eclipsed conformation of butane where the two methyl groups are  syn.  In order to reduce steric interactions, bonds and bond angles deform ever-so-slightly from their ideal values, resulting in strain. Strain results in small barriers to rotation between conformations, which can be measured experimentally and calculated using advanced computational methods we won’t get into. The C1-C2 bond of butane, along the C2-C3 bond of butane not all energy maxima (the peaks on the graph above) have the same energy.   The energy maxima correspond to the eclipsed conformation with both methyl groups  syn   (dihedral angle 0°, strain energy about 5 kcal/mole) and the two remaining eclipsed conformations (dihedral angles 120° and 240°, strain energy about 3.6 kcal/mole). 18 CONCLUSION

22. THANK YOU