This is because:
* The stress falls on the first syllable "syn", which means the second syllable "thetic" is unstressed.
* Unstressed syllables tend to be reduced, with the vowel often becoming a schwa sound (ə).
* The final consonant cluster "tic" is pronounced with the "t" being silent, leaving only the "ik" sound.
Therefore, the final sound of "synthetic" is the ɪk sound, similar to the "ick" in "sick" or "quick."