I have recently made an amazing discovery which will doubtless change the course of history. If I mix orange zest and graphite (by sticking the tip of a mechanical pencil into a clementine peel), the combination cannot be erased. Why is this?
Could you be more specific? Are you just poking a pencil into an orange?
I think the force there would be to the fact that the eraser can’t get into that small hole efficiently with enough friction to rub away the pencil.
Likely because the limonene in the orange oil coats the paper you write on, and the graphite you’ve written with, leaving a slick, eraser resistant surface.
What the hell is d-Limonene? Last I checked, there were just R- and S- enantiomers. Oh well.
Maybe they mean D-limonene, instead of d-Limonene. (btw, what customer cares that it’s dextrorotatory?)
grumbles that he asked and answered his own question
So, OP: Are you getting orange oil on your paper? I’d assume it’d be the orange oil in general, not just the limonene (Yes, I know it’s only one enantiomer, not a racemate, but it’s easier just to say limonene.) that’s cutting down on the friction.
[WAG]
R- and S- are the Fischer Projections? Then you have d- and l- which is similar, but I thought that was only used for Amino Acids?
[/WAG]
I feel like Gary Larson’s “Ginger”:
Blah blah blah orange blah blah blah paper
D- and L- mean “dextrorotatory” and “levorotatory”, respectively, and refer to the direction in which each enantiomer rotates light. Because the light-rotation property is not always linked to the R- and S- stereochemistry (an R- compound may be levorotatory, etc.), D- and L- are used. The body uses mostly L- enantiomers, I think, so that’s probably why you may have seen it only in conjunction with amino acids.
Can’t answer the OP though. Sorry! 
What customer would care if it was r or s? D vs L is easy to tell with a refractometer.
When I was a kid, we all knew that almost any grease or oil, even skin oils, on the paper or eraser would impede a clean erasure. Moisture, too, caused problems, though it might at least dry up while you were still working on that page. A fresh well-kept eraser was valued.
It affected writing too. Sometimes you encountered pencils that had been exposed to some unknown oil in the past and wouldn’t write well, or paper with random spots (often invisible oily hand or finger prints) that were hard to write on.
We often went back and did a “clean-up” immediately before handing in an important paper, in the hope that enough moisture or oil has dissipated to allow some of the messier spots to be tidied up.
Is that lost knowledge now? I feel like an Egyptian temple stonemason teaching young whippersnappers how to dampen stone to cut sharper hieroglyphs.
Do tell. Why would you be stabbing innocent clementines with your lead pencil?
Signed,
My Darling Clementine
Wrong, wrong, wrong.
R and S are absolute stereochemical designations based the actual location of groups around a chiral center – developed by Cahn, Ingold & Prelog.
D and L are designations in the Fischer convention, and are also based on the location of groups around the chiral center. They are only used in amino acid and sugar chemistry, as they are based on the location of specific groups. L is nearly always the same as S in the above system.
(+) and (-) are designations of optical activity: (+) enantiomers rotate the plane of polarized light clockwise, and (-) enantiomers rotate it counterclockwise. While these designations are determined by the chemical structure, they don’t tell you what it is.
d and l (lower-case letters, notice) are obsolete, but still used in commerce. They stand for dextrorotary and levorotary, and they correspond to (+) and (-), respectively.
d-limonene is the common name for the fragrant terpenoid present in orange and lemon oils. For what it’s worth, its IUPAC name is (R)-4-isopropenyl-1-methylcyclohexene.
I want to contradict you, but someone who starts their post off with three “wrongs” probably knows what they’re talking about.
So R and S are accepted by IUPAC, correct? I assume that D and L are from older literature, which would probably explain why I’ve never seen it. My only problem stems from the fact that I’ve never seen lowercase d or l. I’m pretty sure that my book uses capital D and L for dextrorotatory and levorotatory; I’ll report back later. Sorry if my ignorance confused people.
But getting back to my point, why would the consumer care which way it rotated light? What person is going to read that and say that “I don’t want that silly d-limonene! Gimme the (-) enantiomer any day!”
Hah! It’s a terpene, isn’t it?
(If not, crap. I tried to correct you. I’ve just never seen the word terpenoid before to describe those. )
Yes… happens every time when I just gloss over a subject, someone else comes along and says what I meant, but didn’t explicitly state.
IYO, is what Nametag said correct?
(sorry about the 3 posts… thought of things to say after I hit submit.
Heh, it’s sad to get so schooled in GQ
My organic chemistry textbook (2004) uses D and L for Fischer projections and the way Nametag uses d and l, (+) and (-). However, my biochemistry textbook (1990) uses D and L only in the way Nametag uses D and L.
However, the D and L used for Fischer projections is … smaller. It looks like a different font, but I can’t find an appropriate replication on my character map to show you all. Basically, L-alanine is the Fischer projection designation and L-alanine would indicate levorotatory alanine (if there is such a thing; example pulled from ass).
This is probably the source of my confusion, and combined with my lack of attention to capitalisation I think it’s safe to say Nametag is more correct. At any case, I probably should have quoted the passage I was responding to, where someone asked what was d-limonene, because that’s what I was trying to answer with my discussion on dextro- or levo-rotatory. It’s clear I jumbled up the significance of the L and the L when talking about the biochemical qualities.
Sorry, guys, my mistake. I did indeed look in my 2004 textbook, and they use the small uppercase D and L for Fischer’s notation in the biochemistry section.
Whoops. Continue. (Although I think that we’ve already answered the GQ :P)