Dear Bobby Solanki ,

I don't think the QST2 method is your best chance to get the transition state, as it will require having the acetaldehyde-ammonia pre-reaction complex in a proper orientation so it can be properly interploated.

I recommend you to optimize the hemiaminal product, in a conformation that places the O-H bond pointing towards the nitrogen, and then perform a relaxed scan elongating the C-N distance. You should get a maximum that corresponds to the dissociation / bond formation, take that structure as your initial guess for optimizing the transition state.

Hope you find it helpful

Dear Enrique Manuel Arpa,

Thank you for sharing this information with us. I'll attempt to use this data to estimate the transition state.