asp.net web api list of list pass into json ajax

I have web api controller where I try to do something like this:

public IHttpActionResult Get()
    {

        var Rooms = db.Rooms.Select(r => new {
            Id = r.Id,
            Name = r.Name,
            ChairNum = r.СhairNum,
            Requests = r.Requests.ToList()
        }).ToList();

   return Ok(new { results = Rooms });

}

In Model I have this:

public partial class Room
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public Room()
        {
            this.Requests = new HashSet<Request>();
        }

        public int Id { get; set; }
        public string Name { get; set; }
        public int СhairNum { get; set; }
        public bool IsProjector { get; set; }
        public bool IsBoard { get; set; }
        public string Description { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<Request> Requests { get; set; }
    }

I tried to pass this data in service. But I have serialization error. What is the best way to pass the data like in model into json?