You seem to want a numeric sort but are getting a character sort.
a number range would be 0,1,2,3, ... 9,10,11 ...
sorting like everything else with computers is an algorithm. Someone needs to define how it works. When you see a list of files, someone has defined how the list will be sorted. If you compare Windows file sorting to Mac files sorting you will find there are differences.
In the case of files sorting, the files are sorted on characters from left to right. In file sorting the sorting algorithm does not try to determine that files are numbers. All files beginning with a 1 will be sorted together becuase the file sorting althorithm doesn't look at the second character position before grouping all the 1's together.
For what it is worth, there are multple books written on sorting.
how can i sor the files on the IBook with its name starting with numbers as1 &1.1 and so on.
In bookshelf view, you can arrange the items in whatever order you want via the edit button.
In list view, you will have to renumber your items so that the sorting system used by iBooks gives you the results you want, perhaps by padding with zeros, e.g: 001, 002, 010
You might want to try another pdf reader, like GoodReader, and see if it will do things the way you want.