ODOROUS COMPONENTS OF THE NECTAR
The flowers smell less strongly (of vanilla) than do those of Lesser Butterfly-Orchid and they also smell differently because they contain a different set of aromatic compounds:
Lesser Butterfly-Orchid contains the following compounds as odour components of the nectar:
Santolina Triene 19.5%
Benzyl Acetate 0.5%
Lilac Adehyde 0%
Lilac Alcohol 0.2%
Greater Butterfly-Orchid contains the following compounds as odour components of the nectar:
Santolina Triene 01%
Benzyl Acetate 0.01%
Lilac Aldehyde 15.6%
Lilac Alcohol 2.6%
β-Ocimene comes naturally in two slightly differing isomers, the cis- form and the trans- form. They are usually made together but not necessarily in a 1:1 ratio. [
α-Ocimene occurs in neither Lesser nor Greater Butterfly Orchids]. The various Ocimenes are all oils with a delightful scent and used in perfumes but they are unstable in air as is the similar Myrcene (which does not occur in these orchids). Ocimene is derived from the Ancient Greek name for Basil which is κιμον. Ocimenes have anti-fungal properties and are thought to act in plant defence, they are harmful if swallowed, irritating to skin and eyes and toxic to aquatic organisms.
Nerol is another monoterpenoid found in the essential oils of many plants such as Hop and the non-native
Lemongrass and is also used in perfumery. It is isomeric with Geraniol. Nerol readily loses water to become the cyclic monoterpene Limonene, which has two stereoisomers; the racemic mixture of which is called
Santolina Triene is also found within a Mugwort [specifically the non-native
Santolina Yarrow (Artemisia santolina] and also plants from the Sanotlina genus which are small evergreen shrubs found mainly in the western Mediterranean region.
Both Lilac Alcohol and Lilac Aldehyde are found in Lilac flowers, hence their names. They are used in the perfume industry. The Lesser Butterfly-Orchid contains no Lilac Aldehyde and very little Lilac Alcohol, whereas Greater Butterfly-Orchid contains much more. They both contain a Furan moiety (the five membered ring with oxygen) which makes them toxic. (Your Author thinks it amazing how many chemicals used in perfumes are toxic but the folk putting them on their skin seem unaware of this fact).
Because there are 3 chiral centres on the Lilac Aldehyde molecule, there are 23 = 8 differing stereoisomers of Lilac Aldehyde with odour thresholds varying from 0.2ng to 22ng, each smelling slightly differently such as 'sweet and flowery', 'fresh and flowery', 'flowery' and 'pleasant, flowery and fresh'.
There are also 3 chiral centres on the Lilac Alcohol molecule and thus the same number (8) of differing stereoisomers, but this time the odour threshold varies from 2ng to 100ng and the smell from 'green, grassy and fresh', 'sweet', 'flowery', 'odourless', 'flowery, sweet with body', 'herbaceous and slightly flowery' to 'sweet and flowery'.
In both cases your Author knows not which stereoisomers are present in either of the two Butterfly-Orchids.
Benzyl Acetate is a pleasantly sweet-smelling ester which is also found in the flowers of
Jasmine (a genus of vines and shrubs in the Jasninium genus of the Olive family (Oreaceae) which are native to tropical and warm regions of Eurasia). It is used in perfumes and cosmetics and also as apple and pear flovourings in foodstuffs. Various Orchid bee species find the odour attractive and gather it in order to synthesize other pheromones for itself.