This NBC Learn video focuses on chemical bonds by profiling eugenol and isoeugenol, two molecules with identical molecular structures except for the placement of one double bond -- a difference that makes eugenol responsible for the flavor and aroma of cloves, and isoeugenol responsible for the taste and smell of nutmeg.
The Chemical Bond Between Cloves and Nutmeg
BETH NISSEN, reporting
They don’t really stand out in a row or rack of spices: cloves, there between basil and dill, and nutmeg, between ginger and oregano. But for centuries, the most powerful realms of the day risked and lost legions and treasures over these two.
Both were among the most precious and expensive items in the ancient spice trade. Both among the reasons Ferdinand Magellan set out, in 1519, to circumnavigate the globe in search of a new route to the fabled Spice Islands. Only one of his 5 ships returned without Magellan, but with a hold mostly full of cloves.
As for nutmeg, it’s the reason we speak English. A long “Nutmeg War” between the English and the Dutch in the 1600s was settled when the British gave up claims to one of the Spice Islands, and in exchange, claimed from the Dutch the island of Manhattan.
The story of cloves and nutmeg from a molecular perspective is a somewhat less swashbuckling “Tale of Two Molecules,” the bonds they share and one bond that separates them. The two molecules are eugenol and isoeugenol. Their chemical formula tells you what they’re made of: 10 atoms of Carbon, 12 atoms of Hydrogen, and two atoms of Oxygen – the same kind and number of atoms for both.
But this one, eugenol, is what gives cloves their aroma and flavor, and this one, isoeugenol, is responsible for the smell and taste of nutmeg – both spices, but distinctly different spices.
The explanation for this is one of the base rules for understanding molecules: It’s not just how many atoms of what elements make up a molecule, it’s how those atoms are configured, in what structure, and the bonds that hold them together.
In drawings of molecular structures, bonds are represented as lines. But chemical bonds aren’t like teeny strings or ropes or cables. They’re forces: electromagnetic attractions between atoms, specifically, between the electrons in the outer shells of atoms, and their nuclei, their centers.
Forces that hold two or more atoms, like two atoms of hydrogen and one atom of oxygen, together to make molecules, in this case, H2O, or water. So, the lines in molecule structural drawings represent these bonds and indicate the strength of these bonds.
A single line represents a single covalent bond – one atom bonded to another through two shared electrons. A double line indicates a stronger double bond – two atoms bonded together through four shared electrons.
Looking at the structural drawings of eugenol and isoeugenol, you see, in both, single bonds and double bonds, making them identical in number and strength of bonds except for one tiny detail.
If you think of this part here, called the hydrocarbon side chain, as a shoulder, upper arm and forearm, the eugenol molecule has the double bond at the forearm. The isoeugenol has the double bond at the upper arm.
This single difference, not in the kind or strength, but in the placement of one double bond, is enough to make this molecule, eugenol, responsible for the aroma and taste of clove, and this one, isoeugenol responsible for nutmeg.
Just to make things interesting, if you add a double bond here, kind of at the wrist, you get Zingerone, the compound responsible for the specific smell and taste of ginger.
There’s much more to learn about bonds: covalent bonds, ionic bonds, hydrogen bonds. But in understanding molecules, there’s a time, and as eugenol and isoeugenol demonstrate, a place for everything.
Matter makes up everything visible in the known universe, from port-a-potties to supernovas. And because matter is never created or destroyed, it cycles through our world. Atoms that were in a dinosaur millions of years ago — and in a star billions of years before that — may be inside you today.
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