If the compound rotates the plane
of plane polarised light to the right, i e , clockwise direction, it
is called dextrorotatory (Greek for right rotating) or the d-form
and is indicated by placing a positive (+) sign before the degree
of rotation If the light is rotated towards left (anticlockwise
direction), the compound is said to be laevo-rotatory or the
l-form and a negative (–) sign is placed before the degree of
rotation