Hi,
As Rosh replied to you ,
Call transaction EC01 --> Choose structure --> Choose Navigation --> Choose your company code
In addition to it,
Double click on you company code or go to detail , you find the all structure under the company code
you can not see purchasing group over here , because that does is not link to enterprise structure.
To see the purchase group, you need to go - IMG-Material Management- Purchasing- create purchasing group, you can see all list of created purchasing group,
check your purchasing group here
Hope it will help you