When you show a problem, a model of a compound will appear in the window on the left. Carbon atoms are gray, hydrogen is cyan, oxygen is red, nitrogen is blue, and other elements are labeled by their symbol. This model may be moved about by the mouse, and examined from different perspectives. You should then draw a structural formula for this compound in the drawing window on the right, and check your answer.
Problems 9, 11,12, 13 and 15 require use of the wedge drawing tool to indicate configuration, and also attachment of hydrogen (use the X button) to stereogenic centers. Do not use this tool or add hydrogen in other cases.