Stereochemistry|Chair and Boat forms of Six membered ring|By Dr. Pravin S. Patil

0:01 [Music] now stereochemistry of six member rings so the six member rings are more stable than five membering it was proved by so say in 1890 okay in non-planar structure or structure of cyclohexane the valence bonds of all carbons are at tetrahedral angle that means 109 degree to 28 minutes to each other and which are therefore free of angle strain which form is free of angle strand so this chair form see here this chair form is free from angle strain why because each carbon

0:47 attached with hydrogen tetrahydral angle okay so here spk fiberization so carbon attached with different hydrogens and different carbon tetrahedral angles so therefore tetrahedral angle so is free from angle strain now it is a chair form of cyclohexane so labeling first one two three four five and six this way this hydrogen attached with this carbon atoms in cyclohexane now here i am display with this h and h e this h a means axial hydrogen and h means equatorial hydrogen so how

1:33 can we explain this chair form needs excellent equatorial hydrogen see here in this structure this axial above this axial below axial above axial below above below so this is the axial in alternate manner above and below above and below this way similar way equatorial equatorial below above below above below above so this way equatorial also orange in cyclohexane tree so this way you can see here this hydrogen axial this axial again this axial elbow this axial below again this axial label

2:18 is actually below same as equatorial below above below above below and above equatorial hydrogens this way you can explain equatorial and axial position of hydrogen in cyclohexane ring we are also given newman structure of this cyclohexane ring for chair form in chair form so first start with this first carbon first second third fourth fifth and sixth you know you are familiar with newman structure so in first position okay now this this position is axial equatorial equatorial axial similar way axial

3:05 equatorial axial axial equatorial equatorial axial equatorial axial this rearrangement of hydrogen in human form or neumann projection structure okay and here all the hydrogens are 1 0 9 and 28 minute so therefore it is a stagger form okay arrange different stagger form okay so that means very less interaction between these two hydrogens now chair form is mobile form because which can be distorted into variety of shapes like bot form twist spot form or half chair form etc so that's why this chair form is called mobile form

3:51 when the bottom part of the chair form is bent in upward or down bent in downward direction the chair form is transforming to board form now board form when fourth carbon is bent in upward direction so this board form or chair form is converted into bot form similarly when first carbon of this chair form bent into downward direction so this set is converted into both form but this structure is more preferable here this chair form is free from angle strain and bone opposition strain so therefore it is a it has less energy

4:38 and more stable and it is this point minimum in energy diagram at point a during transformation some angular distortion is required because several bonds have to be rotated at the same time when when chair form convert into board form the bot form of cyclohexane molecule has no angle strength that means both form is also free from angle strain okay only angle distorted what is a free from angle strain but it has higher potential energy and it is described in energy diagram at point d and this higher

5:26 potential energy due to bone opposition strand bond opposition stand now what form there is a bond opposition strain involving the four pair of hydrogens at the side of the board a pair of upper side and downward side this way upper side and downward side okay just interact with each other so therefore this create a bond opposition strain okay you can also see here the newman projection structure of this bot form so first carbon [Music] second third fourth fifth and sixth now here this circle means rear carbon and its hydrogen it's completely

6:12 eclipsing with front carbon and its hydrogen okay so you cannot visualize this rear carbon and its hydrogen so therefore the eclipsing and due to this eclipsing what happened interaction between this hydrogen so bone opposition strain is due to this eclipsing structure in what form here also in upper hydrogen the distance between this upper hydrogen is 1.8 angstrom so it is very close and this hydrogen is called flagpole hydrogens and the interaction between this hydrogen is called flagpole intellection so there is a strain mainly due to a pair of top hydrogens

6:57 which are about 1.8 angstrom apart while the sum of wonder was ready of two hydrogens is 2.4 angstrom that means when hydrogen molecules the distance between hydrogen molecule is 2.4 okay and distance between two hydrogen in both form is 1.8 so it is less as compared to an hydrogen molecule so therefore it is very close so more interaction more repulsion so therefore reduces its stability and increasing its energy so therefore it is also called bow spirit flagpole interaction okay the carbon carbon bonds are exactly eclipsed

7:43 thus there is a significant torsional strain or bone position in the molecule okay you can also say torsional strain or bone opposition strain both are same thus repulsion in sigma electronic cloud of this hydrogen diesel in instability of board conformation this way you can explain instability of what form of cyclohexane you