No officers named Nechenskii. As noted above, it's Chechenskii.

Aleksandr Nikolaevich Chechenskii - a junior officer in and out of the Nizhnii-Novgorod (or Nizhegorod) Dragoons several times 1796-1806. (The Nizhegorod Dragoons habitually served in the Caucasus and had numerous local nobles in the officer ranks.) 23 July 1806 rejoined the army as a Sub-Lieutenant in the Grodno Hussars, soon became an adjutant to Lt. Gen. Raevskii, awarded St. Anne 2nd Class in 1809 (war with Sweden), left the army again 9 December 1811, rejoined 5 July 1812 in the Grodno Hussars but attached to Maj Gen Yermolov (chief of staff 1st Western Army). By December 1812, as a captain, he was commanding the 1st Bug Cossack Regiment in Davydov's partisan force. 11 January 1814 transferred to the Life-Gds Hussars but still acted as commander of the Bug Cossacks; at fall of Paris 18 March 1814. As a lieutenant colonel, finally took 6 month's leave 6 May 1814. As a full colonel, 1 January 1816 given command of the Lithuania Lancer Regiment. In the 1820s, a major general of light cavalry, without holding any particular duties.

The only other Chechenskii of note I have information on was Valerian Nikolaevich Chechenskii, who may or may not have been a relative. He served in the Tiflis Jagers (later Grenadiers) in the 1840's and '50's.