Loan words borrowed from the middle/end of original word?
This article (p. 60-61) provided the reason 氡 (radon) is based on the latter syllable. In summary, this was the result of an argument between Chinese chemists appointed to element naming in the early 20th century. Those that argued radon should not be given a pronunciation similar to 鐳 (radium) so as to avoid confusion won. The lost faction argued  reflects the origin of radon from the alpha decay of radium better.

Wikipedia argues 砷 (arsenic) and 鋁 (aluminium) came from the second syllable of the English equivalent. 碘 (iodine) came from the third.

Another example I can think of is the Taiwanese translation of Al-Qaeda, 蓋達組織 (not a character per se). That is so because 'al-' is an Arabic definite article ('the') and Chinese does not have a grammatical equivalent, therefore omitted. However, the translation 阿爾蓋達組織 is still perfectly valid.