jQuery .extend not interpolating a config value. why?

jQuery .extend not interpolating a config value. why?

I have something simple I believe, yet I am getting js error.
$.extend(hashONE,{options.item1 : options.item2});
also tried:
$.extend(hashONE,{options[item1] : options[item2]});
also
var opt = {options[item1] : options[item2]};
$.extend(hashONE, opt);
All these generate an error on the "."
I must be daft, this is suppose to be easy :-)