Cinnamaldehyde
H H
\ /
C--C H O
/ \ | //
H--C C--C==C--C
\ / | \
C--C H H
/ \
H H
cinnamaldehyde (trans isomer pictured)
Cinnamaldehyde, 3-phenylpropenal, is an aldehyde and the compound that gives cinnamon its flavor, odor, and general cinnamon-ness.