To debug what happened in #1, display what your alias aliasname
actually is, by:
alias aliasname
You will get: alias aliasname='Hello'
So, your alias is the
same as typing the invalid command: Hello
What happened was that you used
backquotes, which executed the echo inside them first,
then defined aliasname!!!
Maybe you wanted 'regular' 'forward' quotes. See also $(cmd) in bash syntax.
Welcome to the 'secret'

world of: the bash topics of quoting and command substitution!!!
You (&I!!!) can use [code]terminal stuff[/code], to make post look nice, like#3. Also, at top, mark thread 'solved' when done here. Let us know.