Stability of different tautomers of vitamin C

[![enter image description here](https://i.stack.imgur.com/VToWC.jpg)](https://i.stack.imgur.com/VToWC.jpg)


Above all four tautomers represent Vitamin C (Ascorbic acid)


So here are some basic rules that I learnt.


1.Usually keto form is more stable due to bond enthalpy considerations


2.Enol form is stable if :



```
  (1)It is aromatic (diamagnetic ring current stabilization)
  (2)It is highly conjugated
  (3)it has 5/6 membered intramolecular hydrogen bonding
  (4)keto has highly acidic alpha-hydrogen
  (5)keto is cyclic 1,2 diketo
  (6)keto is 1,3 dicarbonyl

```

Using these rules I was able to conclude :


* 4th structure is least stable
* 2nd structure is 2nd least stable


But for the 1st and 3rd structures both satisfy 2(3) point given above.


What is the final stability order?


