apollo an analogue is usually classed as a compound similar in structure, but with different functional groups attached.
MDMA is to MDA the same way 5MeSDMT is to 5MeODMT and ephedrine is to amphetamine. In the former it is a different amine (sec -> primary) the second has a sulphur substituted for an Oxygen and with ephedrine it is simply the addition of an OH group.
Homologues are compounds which have different carbon lengths to the parent compound. A simple example is to compare MBDB to MDMA. MBDB (eden, methyl J etc.) is 1 carbon longer in the alkyl chain - 4 instead of 3 - than MDMA. Otherwise the molecule is chemically identical, as the amine is off the 2nd carbon and the ring is the same etc. Altering the carbon chain length on an amine (methylamine -> ethylamine), or lengthening the chain of a methoxy substitute to an ethoxy are also examples of homologues.
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In regards to LSD fragility; maybe a better experiment would be to halve your liquid/trips and store one half in supposedly ideal conditions and the other half as kewl suggests - on the window ledge. That way you have the original "well kept" version to compare strength etc. Of course it's impossible to take subjectivity out of the equation (set and setting), and any degradation would likely change with concentration, but if assayed it should be obvious if there's a significant drop in potency.
LSD is a geometrically unique molecule when comparing it to other familiar tryptamines and phenethylamines. To look at it simply, the structure contains some rather unstable positioning of the attached atoms. An analogy could be a spring loaded electrical switch where if it is pushed past a certain point the switch throws and the contacts move with the releasing spring. With molecules, structural changes can occur because attached groups like to distance themselves from similar charged groups and move closer to oppositely charged groups. Other factors influence positional preference such as the bulkiness of the atoms. Sometimes positioning is an overall compromise, meaning several bonds between atoms are strained (higher energy - less stable)
As referenced below in Shulgins quote, with LSD the carboxamide group and and asociated hydrogen switch positions relative to the rest of molecule, producing iso-LSD. All it takes is for a bit of energy to push the switch. Shulgin states this eperimisation is catalysed by light or alkaline conditions. The double bond adjacent to the carboxamide is also susceptable to addition of an OH group catalysed by UV/visable light or free radical reactions (e.g. chlorine).
Structually then, LSD is somewhat fragile
It is also important to appreciate the potency of LSD. As a very rough comparison, comparing 100ug of LSD to 100mg of MDMA, LSD is effectively 1000 times more potent. Therfore one of the things which shouldn't be forgotten when thinking of a relatively fragile molecule like LSD, is the relative concentration of the form; microdot, blotter gel. Even liquid.
When considering a small amount of concentrated liquid, approx. 1 gram of tartrate salt dissolves in 1mL of H2O (LSD being very water soluble)
1g LSD + 1mL of H2O -> LSD solution concentrate of 1g/ml or 1000g/ L
An arguably large dose for many non-regular users is say = 200ug
If 1 drop of concentrate = approximately 50uL of liquid
1drop as 50uL x 1000g/L = 0.05g = 50mg
50mg / 1 High dose (200ug) therefore = 250 high doses !!
So liquid acid sold or consumed by the drop is usually very diluted, sometimes by as much as 1:1000 or more using the above model. That means for the given physical mass of a std dose, the LSD content is normally a very small %. Levels of destructive chlorine or other reactive species therefore do not have to be present in large amounts to do damage e.g. concentration of chloride ions in a drop of tap water.
Shulgins notes as mentioned by apollo
From TiHKAL # 26
LSD is an unusually fragile molecule and some comments are in order as to its stability and storage. As a salt, in water, cold, and free from air and light exposure, it is stable indefinitely. There are two sensitive aspects of its structure. The position of the carboxamide attachment, the 8-position, is affected by basic, or high pH, conditions. Through a process called epimerization, this position can scramble, producing isolysergic acid diethylamide, or iso-LSD. This product is biologically inactive, and represents a loss of a proportionate amount of active product. A second and separate point of instability is the double bond that lies between this 8-position and the aromatic ring. Water or alcohol can add to this site, especially in the presence of light (sunlight with its ultraviolet energy is notoriously bad) to form a product that has been called lumi-LSD, which is totally inactive in man. Oh yes, and often overlooked, there may be only an infinitesimal amount of chlorine in treated tap water, but then there is only an infinitesimal amount of LSD in a typical LSD solution. And since chlorine will destroy LSD on contact, the dissolving of LSD in tap water is not appropriate
J Anal Toxicol 1998 Oct;22(6):520-5 (Medline (PMID=9788528))
Stability study of LSD under various storage conditions.
Li Z, McNally AJ, Wang H, Salamone SJ.
A controlled study was undertaken to determine the stability of LSD in pooled urine samples. The concentrations of LSD in urine samples were followed over time at various temperatures, in different types of storage containers, at various exposures to different wavelengths of light, and at varying pH values. LSD concentrations were measured quantitatively by the Abuscreen RIA and by HPLC using a fluorescence detection method. Good correlation was observed between the immunoassay and the fluorescent integrity of the LSD molecule. Thermostability studies were conducted in the dark with various containers. These studies demonstrated no significant loss in LSD concentration at 25 degrees C for up to 4 weeks. After 4 weeks of incubation, a 30% loss in LSD concentration at 37 degrees C and up to a 40% at 45 degrees C were observed. Urine fortified with LSD and stored in amber glass or nontransparent polyethylene containers showed no change in concentration under any light conditions. Stability of LSD in transparent containers under light was dependent on the distance between the light source and the samples, the wavelength of light, exposure time, and the intensity of light. After prolonged exposure to heat in alkaline pH conditions, 10 to 15% of the parent LSD epimerized to iso-LSD. Under acidic conditions, less than 5% of the LSD was converted to iso-LSD. We also demonstrated that trace amounts of metal ions in buffer or urine could catalyze the decomposition of LSD and that this process can be avoided by the addition of EDTA. This study demonstrates the importance of proper storage conditions of LSD in urine in order to insure proper analytical testing results over time.
"Table II illustrates that fluorescent light can cause decommposition of LSD in transparent containers when they are placed in close proximity [15 cm] to the light source. Under these conditions, the half-life of LSD was approximately 4 weeks. As the distance between the source of fluorescent light and the samples increased, the percent of LSD decomposition decreased. The results demonstrate that LSD can withstand normal room light conditions at a constant temperature of 25°C for 1 week without noticeable structural change."
Sorry bout the long post everyone, hope there was something in it worth the read