Do one of the following to flip (mirror) the smaller of two fragments that are connect by a selected bond:
Choose Arrange > Flip Smaller Fragment.
Choose Flip Smaller Fragment from the Drawing Area pop-up menu.
Press Ctrl+F.
Note: This command is not available if the entire structure is selected. Use the Lasso tool to select the bond of interest or hover either selection cursor over the bond and right-click to open the Drawing Area pop-up menu.