The LCGC Blog: Stop and Smell the Geraniol

When I was growing up in rural Michigan, my oldest aunt on my mom’s side had the loveliest little flower garden. Brick pathways led through a white wooden fence to a backyard oasis of beautiful rose bushes. During family parties, my cousins and I would run through the yard without a care in the world. I always thought her flowers were stunning, but only as an adult have I realized the amount of time she must have spent tending to those rose bushes. She must have cared for them as she cared for her nieces, nephews, and grandchildren, with a watchful eye and a gentle supportive hand. To this day, long since my aunt left us, I associate all things roses–their sight and especially their smell–with my darling aunt.

Gorgeous Victorian Large Botanical Image | Image Credit: © The Graphics Fairy - https://thegraphicsfairy.com/free-vintage-images-lovely-pink-rose/

Little did I know all those years ago that I would become a chemist with a budding interest in scent and fragrance. Over the last half-year, while on research sabbatical, I have taken myself on a self-directed journey to learn all that I can about fragrance molecules. My reading list has included Turin’s informative “The Secret of Scent” (1), Mandy Aftel’s beautifully written and photographed “Museum of Scent”, and countless literature articles on the science of scent, synthesis of fragrance molecules, and the analytical measurement of smells (the collections edited by Pybus & Sell and Marsili have organized incredible resources). I’ve also attended several workshops to gain more hands-on experience with the language and world of scent creation and analysis. The Sensory Directed Analysis (SDA) workshop at Gerstel is a must for anyone interested in analysis of fragrances and flavors (5). Soon, I plan to visit Mandy Aftel’s Museum in Berkeley, where she has collected an outstanding number of natural specimens used in fine fragrance (6). Most recently, I attended a week-long fragrance intensive at the Institute of Art and Olfaction (IAO) in LA. Each day at the IAO, we focused on smelling pieces of the formula that make up different genres of fragrances. From fougeres to chepres and florals to fruits and woods to musks, we smelled countless blotters of individual fragrance molecules, learning how and when to combine ingredients in a formula to create a given effect.

My favorite days were the flower days. For hours, we smelled beautifully orchestrated chemical combinations that recreated the exact nuance of flowers fresh from the garden. Passing around the blotters, my brain first picked up on the rose scent inches away from my nose. A flash of my aunt’s colorful pink and red rose bushes in her bright green yard popped into my head. How amazing that with just a few chemicals combined together, a vibrant image and a core memory could be retrieved.

Image Credit: © Amber Hupp

Surprisingly, the breakdown of a rose’s scent can be quite simple. Combine citronellol, phenyl ethyl alcohol (PEA), geraniol, and a touch of beta ionone, and you have a rose! Of course, each perfumer will create their own twist based on their own preference to make a nuanced rose flower just waiting to tantalize your nose. Adding gamma decalactone can add a peachy flair, cis-3-hexenal can turn the rose a bit greener, while frambinone adds a sweet raspberry note. It is quite incredible though, that to recreate the essence of rose, one only needs four compounds. The ratio between citronellol and PEA will determine what type of rose is produced. A higher amount of citronellol creates a more typical natural rose, while a higher PEA amount creates a softer, greener rose. Increasing the beta ionone in the formula shifts it to a tea rose.

I am no perfumer, yet I wanted to try my hand at creating a rose accord in the IAO lab. For my rose, I used equal parts citronellol (rosy, mosquito repellent) and PEA (honey, sweet) with about one-quarter the amount of geraniol (herbal, mosquito repellent), an eighth of beta ionone (fresh flower, rose, violet), with a dash of eugenol (clove) and beta damascone (sweet plum). The combination of molecules I combined certainly passes for a lovely rose flower, and in fact, it continues to remind me of childhood memories in my auntie’s backyard. Even my daughter and her Girl Scout troop agreed that I made a wonderful scent, some even commenting that it smelled even better than the rose essential oil to which we compared. Who knew that tweens can be flattering after all?!

Image Credit: © Amber Hupp

As a chromatographer, I had been itching to run the accords I created. Essentially, I wanted to use my technical tools to help me understand the rose fragrance more. Could I separate and detect these components as easily as it seemed in the literature? How does my rose accord vary in composition from the natural rose oil? Could I detect the components that I added at a two percent concentration? I turned to gas chromatography (GC) to discover some answers.

My GC system is currently home to a polar column for other projects happening in the Hupp Lab. I decided to create a very simple temperature program and dedicate in-between student time on the instrument. The resulting chromatogram is almost as elegantly simple as the smell I created. Six simple peaks, varying in height based on the concentration in which I added them to my vial. And those components at the lowest concentration? Small peaks, but still with great signal-to-noise ratio (S/N) and a mass spectrum that matches my internal database. Really, what more could a girl ask for?

Image Credit: © Amber Hupp

According to neuroscientists, odor memories can be some of the strongest we possess (7). It is still amazing to me that with the right combination of fragrant molecules, we can be transported to a time we thought lost, with memories of certain moments in time rushing right back. That combination of just a few fragrant molecules created just the right key to unlock the perfect memory at my aunt’s house. Of a sunny summer day with my family. Of youthful innocence surrounded by people who have since left us. A time in my life when I really could just stop and smell the roses. I feel lucky that I was able to experience these memories again, of a moment lost to the passage of time. My journey into the world of scent has just begun, but I have to wonder… what other memories might I unlock as I continue to explore?

Amber Hupp is a Professor of Chemistry at the College of the Holy Cross in Worcester, MA. She has served on the ACS Subdivision of Chromatography and Separations Chemistry since 2014, and is currently finishing her term as Past-Chair. Research in the Hupp Lab centers on understanding the chemical composition of biodiesel and diesel fuels using gas chromatography and chemometric methods of analysis, specifically focused on efficient separation of fatty acid methyl esters (FAMEs) using various column chemistries. Direct correspondence to: ahupp@holycross.edu

References

(1) Turin, L. The Secret of Scent: Adventures in Perfume and the Science of Smell; Harper Perennial, 2007.

(2) Aftel, M. The Museum of Scent: Exploring the Curious and Wondrous World of Fragrance; Abbeville Press, 2023.

(3) Pybus, D. H.; Sell, C. S. The Chemistry of Fragrances: From Perfumer to Consumer; RSC Paperbacks, 1999.

(4) Marsili, R. Sensory-Directed Flavor Analysis; CRC Press, 2019.

(5) What is Sensory Directed Analysis? Gerstel 2025. https://www.gerstelus.com/what-is-sda/ (accessed 2025-03-13)

(6) Homepage. Aftelier Perfumes 2025. https://www.aftelier.com/ (accessed 2025—03-13)

(7) Mouly, A.; Sullivan, R. Memory and Plasticity in the Olfactory System: From Infancy to Adulthood. In The Neurobiology of Olfaction; CRC Press/Taylor & Francis, 2010.