Dutch scientist, J. van't Hoff and French scientist, C. Le Bel both independently in 1874 pointed out that the four valencies of carbon do not lie in a plane but are directed towards the four corners of a regular tetrahedron. In other words, carbon is tetrahedral . The angle between any two adjacent valencies is 109.5⁰ which is also called the tetrahedral angle . Here, the thick line represents the bond above the plane of the paper and towards the observer, the dotted line represents the bond below the plane of the paper and away from the observer while the normal solid lines represent the bonds in the plane of the paper.