Trying to open a door so far then stop

Trying to open a door from closed to 90 degrees open and then stop.

I can rotate the object but it keeps going around in 360, I need it to stop.

Have below but just gives errors and Im not sure where I am going wrong.

using UnityEngine; using System.Collections;

public class opendoor : MonoBehaviour {

 public int rotatespeed=40;
 public float i=0;
 Vector3 objpos = new Vector3 (0,i,0);    

 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {
     if(objpos >= Vector3(0,-90,0)) 
             {
                     transform.Rotate (Vector3.down * Time.deltaTime * rotatespeed);
                     i+=1;
             
             } 

     else     {

             }
 }

}