Dictionary<string, Book> dict = myCollection.ToDictionary(x => x.BookName, y => y);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
     class Book
     {
          public string BookName { set; get; }
          public int Price { set; get; }
          public int Year { set; get; }
     }

     class Program
     {
          static void Main(string[] args)
          {
               List<Book> books = new List<Book>();
               books.Add(new Book() { BookName = "Властелин Колец", Price = 200 });
               books.Add(new Book() { BookName = "Три мушкетера", Price = 300 });
               books.Add(new Book() { BookName = "Гарри Поттер", Price = 400 });

               Dictionary<string, Book> dict = books.ToDictionary(x => x.BookName, y => y);
          }
     }
}