trans-3-hydroxy- cyclobutanecarboxylic acid methyl ester

trans-3-hydroxy- cyclobutanecarboxylic acid methyl ester

Example 47
Preparation of amines (for Example 16 and 43) and alcohols (for Example 7 and 9)
Example 47-1 : 4-Hydroxy-2,2-dimethylbutyric acid ethyl ester

A mixture of dιhydro-3,3-dιmethyl-2(3/-/)-furanone (10 mmol, 1 14 g), aqueous 1 M KOH solution (10 mmol) and one drop of phenolphthalem indicator (0 5% w/v in EtOH/water (1 1)) is stirred at 105 ⁰C for 3 5 hours The mixture is cooled to ambient temperature and concentration under reduced pressure To the residue is added 10 ml_ of EtOH To the solution is added 50 ml of Et₂O and the solid isolated by filtration and dried under 100 mbar at 50 ⁰C to give potassium 4-hydroxy-2,2-dιmethylbutyrate (1 21 g, 71 %) 1H NMR (400 MHz, c/₅ DMSO) δ ppm 0 96 (s, 6 H), 1 47 (t, J = 5 54 Hz, 2 H), 3 43 (t, J = 5 54 Hz, 2 H)
To a solution of potassium 4-hydroxy-2,2-dιmethylbutyrate (1 92 mmol, 327 mg) in DMF (6 ml_) is added ethyl iodide (2 30 mmol, 359 mg) The reaction mixture is stirred for 2 hours, and quenched with saturated ammonium chloride solution The product is extracted three times with EtOAc The combined organic layer is washed with aqueous 0 1 M HCI then brine, dried over Na2SO4, filtered, concentrated under reduced pressure to give 4-Hydroxy-2,2- dimethylbutyπc acid ethyl ester (520 mg) contaminated with DMF
1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1 22 (s, 6 H) 1 26 (t, J = 7 06 Hz, 3 H) 1 82- 1 85 (m, 2 H) 1 91 (brs, 1 H) 3 69 (t, J = 6 55 Hz, 2 H) 4 13 (q, J = 7 06 Hz, 2 H) Example 47-2: fraπs-3-hydroxy-cyclobutanecarboxylic acid methyl ester

To a solution of cis-trans mixture of 3-hydroxy-cyclobutanecarboxylic acid methyl ester (1 .30 g, 10 mmol) in DMF 13 mL is added NaH (50% in oil, 720 mg, 15 mmol) at 0 ⁰C. After stirring at 0 ⁰C for 15 minutes, benzyl bromide (1.43 ml, 12 mmol) is added at 0 ⁰C. The mixture is stirred at room temperature for 2 hours and quenched with H2O. The solution is extracted with EtOAc. The organic layer is washed with H2O and brine, dried over MgSO4 and concentrated under reduced pressure. The residue is purified by silica gel column chromatography (eluent; hexane / EtOAc) to give trans-3-benzyloxy-cyclobutanecarboxylic acid methyl ester (340 mg, 15.4%). TLC (hexane/EtOAc, 5:1 ) Rf 0.40. 1 H NMR (400 MHz, chloroform-d) δ ppm 2.26-2.34 (m, 2H), 2.48-2.52 (m, 2H), 3.02-3.06 (m, 1 H), 3.69 (s, 3H), 4.26-4.33 (m, 1 H), 4.42 (s, 2H)₁ 7.27-7.35 (m, 5H).
A solution of frans-3-benzyloxy-cyclobutanecarboxylic acid methyl ester (680 mg, 3.09 mmol) as 0.05 M solution in MeOH is pumped through the H-Cube™ flow hydrogenator fitted with a 10 mol% Pd/C catalyst cartridge heated to 40 ⁰C at 10 bar. The flow rate is set at 1 ml/min. The solvent is removed under reduced pressure to give trans-3-hydroxy- cyclobutanecarboxylic acid methyl ester (380 mg, 94.5%); TLC (hexane/EtOAc, 1 :1 ) Rf 0.38. 1 H NMR (400 MHz, chloroform-d) δ ppm 2.18-2.25 (m, 2H), 2.55-2.61 (m, 2H), 3.01-3.08 (m, 1 H), 3.70 (s, 3H)₁ 4.53-4.61 (m, 1 H).


 http://www.google.com/patents/WO2009071509A1?cl=en

सुकून उतना ही देना प्रभू, जितने से जिंदगी चल जाये।औकात बस इतनी देना,कि औरों का भला हो जाये।...........

P.S. : The views expressed are my personal and in no-way suggest the views of the professional 

body or the company that I represent.

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1-{[Benzyloxycarbonyl-(2-methoxycarbonyl-ethyl)-amino]-methyl}- cyclopropanecarboxylic acid ethyl ester

.

 

 Step 1. To a stirred solution of compound 2 as shown below (2.2 g, 15.37 mmol) compd 2

 in THF (25 mL), was
added methyl acrylate (1.39 g, 16.14 mmol) dropwise at 0 °C and the mixture slowly
warmed to room temperature. After stirring for 3 h at this temperature, no starting material
remained as indicated by TLC. The reaction mixture was diluted with cold water (40 mL)
and extracted with ethyl acetate (3 × 20 mL). The combined organic layers were washed
with water (2 × 50 mL), dried over anhydrous Na2SO4 and concentrated at 40 °C under
vacuum to give 1-[(2-methoxycarbonyl-ethylamino)-methyl]-cyclopropanecarboxylic acid
ethyl ester (3) as a liquid (2.61 g, yield 74%). The crude material was used directly for the
next reaction.


 Step 2. To a stirred solution of compound 3 (2.5 g, 10.91 mmol) in dichloromethane
(25 mL), was added triethylamine (1.66 g, 16.37 mmol) at 0 °C followed by the addition of
benzyl chloroformate (2.04g, 12.01 mmol).The mixture was stirred at 0–5 °C and the
reaction monitored by TLC. After 3 h, the starting material had disappeared and the reaction
was quenched in ice water (50 mL). The product was extracted with ethyl acetate (3 x 25
mL). The organic layers were collected, combined, washed with cold water (2 × 25 mL),
dried over anhydrous Na2SO4 and concentrated at 40 °C under vacuum to give the title
compound (3.17 g, yield 80%);

 1H-NMR (DMSO-d6, 300 MHz): δ 0.8–1.0 (m, 2H, 2 × CHc-propyl), 1.0–1.2 (m, 5H, 2 × CH c-propyl and CH3CH2O-), 2.45–2.55 (m, 2H,CH2CO2Me), 3.5–3.65 (m, 7H, 4 × CH N-methylene and CH3O-), 3.95–4.10 (m, 2H,CH3CH2O-), 5.06 (s, 2H, 2 × benzylic methylene), 7.3–7.5 (m, 5H, 5 × CH arom);

MS (CI):364.1 (M+1, 100%); Elemental Analysis found: C, 62.53; H, 6.90; N, 4.04 C19H25NO6
Requires C, 62.80; H, 6.93; N, 3.85.

सुकून उतना ही देना प्रभू, जितने से जिंदगी चल जाये।औकात बस इतनी देना,कि औरों का भला हो जाये।...........

P.S. : The views expressed are my personal and in no-way suggest the views of the professional 

body or the company that I represent.

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He was only in first standard in school when I was hit by a deadly one in a million spine stroke called acute transverse mylitis, it made me 90% paralysed and bound to a wheel chair, Now I keep him as my source of inspiration and helping millions, thanks to millions of my readers who keep me going and help me to keep my son happy

////////

Synthesis of rotigotine-2-Azidopropionate

 

¹H NMR (Varian, 500 MHz, 10 mg/mL CDCl₃) showed peaks at 4.203 ppm CH₃CH(N₃)— (q, 1H) and 1.642 ppm CH₃CH(N₃)— (d, 3H).

 https://www.google.com/patents/US8383093

Example 5 Synthesis of rotigotine-2-Azidopropionate

In a 100 mL round bottom flask was placed 2-azidopropionic acid (251 mg, 2.02 mmol, 1.3 equiv.—in 3 mL of DCM), rotigotine (500 mg, 1.55 mmol, 1 equiv.), and 4-DMAP (249 mg, 2.02 mmol, 1.3 equiv.—in 6 mL of DCM) and the mixture was allowed to stir under argon. The solution was cooled by placing the flask in an ice-water bath for 5 min. To the solution, DCC was added (421 mg, 2.02 mmol, 1.3 equiv.). The progress of the reaction was followed by reversed phase HPLC. Following overnight stirring at room temperature, additional 2-azidopropionic acid (126 mg, 0.65 equiv.) in 2 mL of DCM and 4-DMAP (124 mg, 0.65 equiv.) were added to the reaction mixture, followed by DCC (211 mg, 0.65 equiv.). The solution was allowed to stir at room temperature for another 3.5 hours. HPLC result shows 94% of conversion to ester. The reaction mixture was filtered, and the filtrate was concentrated to dryness on a rotary-evaporator. The crude product was then purified by silica gel chromatography. The crude product was dissolved in hexane-ethyl acetate (6 mL, 4:1 v/v), and then loaded on to a 300 mL Silica Gel Column (30 mm id). The column was eluted with a hexane-ethyl acetate (4:1 v/v). The fractions (10 mL each) were analyzed by TLC and reversed phase HPLC. The product fractions were pooled, evaporated by rotary-evaporation, and then dried in vacuum overnight. Yield: 307 mg.

¹H NMR (Varian, 500 MHz, 10 mg/mL CDCl₃) showed peaks at 4.203 ppm CH₃CH(N₃)— (q, 1H) and 1.642 ppm CH₃CH(N₃)— (d, 3H).

सुकून उतना ही देना प्रभू, जितने से जिंदगी चल जाये।औकात बस इतनी देना,कि औरों का भला हो जाये।...........

P.S. : The views expressed are my personal and in no-way suggest the views of the professional 

body or the company that I represent.

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LIONEL MY SON

He was only in first standard in school when I was hit by a deadly one in a million spine stroke called acute transverse mylitis, it made me 90% paralysed and bound to a wheel chair, Now I keep him as my source of inspiration and helping millions, thanks to millions of my readers who keep me going and help me to keep my son happy

• 10 Great Balinese Fruits

  Top 10 Tropical Fruits To Try In Bali

  
  

  
  

  
  
  
  Fruits in Bali come in a wide variety and are a feast for your eyes and taste buds, with striking and sometimes unusual textures, colours, shapes and sizes. Although several types share much resemblance with those that you find in other places across Southeast Asia, there are some varieties that can only be found here in Bali. This small island eight degrees south of the equator features different terrains that serve as favourable growing places for such fruits. Take the Balinese salak for example, an odd-looking but delicious fruit that is widely grown in the eastern Bali village of Sibetan, Karangasem regency.
  The island’s volcanic highlands allow fertile plains and village plantations to produce a bounty of these exotic and tasty delights. Make most out of your holiday in Bali by pleasing your senses – discover and try as many Balinese fruits as you can. Here is our list of top 10 tropical and exotic fruits to try in Bali. And if you dare, check out how the locals go further with their beloved fruits by adding them as main ingredients in exotic preparations of salads and dishes – you won’t find such an experience elsewhere!
  
  
  
• 
  
• 

  Durian

  
  

  Duren
  The fruit most locals love and most foreigners hate. But like the majority of unusual things, it’s an acquired taste. There are three types of people when it comes to the Durian: die-hard lovers, haters, and those in between who love the taste but can’t bear the smell for too long. The powerful aroma has led to the fruit being banned from hotels and airplanes, and locals know that driving some home from a market or roadside stall will have their car reeking of durian for a week! Opening up one of these heavily spiked melon-sized fruits requires much care and experience – a roadside vendor will scan for a faint line to position his blade then easily crack it open to reveal the fleshy white, to deep yellowish pods. The texture and taste: creamy and sweet, means that there is a good reason for durian-flavoured ice cream. The notorious smell: to some, invigorating, sweet, or even okay… and for many others, putrid, rotten, or simply ‘the toilet is broken’! Lovers of blue cheese can try an exchange with the local villagers and get pretty much a very similar response.

  
  

  
  
  
  
  
  
  

  Mangosteen

  
  

  Manggis
  Those who have travelled to other Southeast Asian countries may have already encountered and tried the mangosteen. Pleasant to all, the round, apple-sized and deep purple fruit is easily cracked opened by pressing between both palms, and caution is to be taken as the rind exudes a reddish sap that can stain clothes. The reddish stains on your palms resemble blood at a glance, hence its nickname the ‘blood fruit’. While the white inner flesh is the prize, a recent trend has surfaced in drying up the rinds and making them into health teas, due to its claimed high antioxidant content. Mangosteen is also known in local traditional medicine as a remedy for skin and digestive problems. The juicy flesh sections contain slightly fibrous and inedible seeds, and most will agree that one is never enough. The evergreen trees are largely grown in the highland regions of Tabanan in Bali’s west, and the Bangli regency on the island’s east.

  
  

  
  
  
  
  
  
  

  Salak

  
  

  Snake/Snakeskin Fruit
  This odd-looking fruit deserves its moniker, with skin resembling tiny snake scales from up close. The fruit’s colour ranges from reddish to dark brown, and it grows in clusters on very spiny palm-like trees – not a pleasant or inviting sight. But once harvested and in your hotel room fruit basket, they are smooth and tempting. Oval to round, the fruit has a pointed top that eases squeezing and is peeled by hand. After revealing the three pale yellow lobes, you still need to rub off a thin layer of silky membrane before enjoying the moist and crunchy treat. The largest lobe contains a hard black seed – hazardous to first-timers’ teeth. Texture and taste: sweet and slightly starchy consistency, a cross flavour between pineapple and Royal Gala apples. One type of Bali’s salak has recently been made into wine by farming cooperatives in Karangasem, East Bali. You’ll come across the fruit in almost all traditional markets and supermarkets.

  
  

  
  
  
  
  
  
  

  Rambutan

  
  

  Buluan
  Like the durian, this fruit is straightforwardly named, meaning ‘hairy’ in the local tongue. They grow in clumps on trees that are commonly grown in village backyards in Bali’s rural areas. Green and yellow when young and a bright red when ripe, they reveal a soft and cloudy white flesh with oval seeds. Over a dozen types of salak are available, from long-haired types with very juicy flesh, to dry-looking short-haired ones that are smaller, rounder and with a lesser moist content. You’ll know you are enjoying top-quality rambutan whenever the skin is easily opened; the flesh is sweet and succulent and easily separates from the seed. When buying a bunch from a traditional roadside fruit vendor up in the mountains or at the market, be cautious of black ants that naturally favour the fruit and tree’s sap – they cling on within the leaves and fruit’s hairs even after it is washed.

  
  

  
  
  
  
  
  
  

  Boni

  
  

  Buah Buni
  These are considered wild berries, but can be found in fruit markets and warungs island-wide. Grown on shrub-like trees, the buah buni bear clustering bunches of small and round berries, white, reddish and black in colour. While easily enjoyed as it is, with a taste ranging from biting sour to sweet, the locals are fond of preparing the buni as a rujak or salad mix, with a blend of sugar, chilli, shrimp paste and salt. High in vitamin C, it is also locally known as a remedy for hypertension.

  
  

  
  
  
  
  
  
  

  Soursop

  
  

  Srikaya
  The ‘sour’ in its name is there for clear reason. Soursop is widely grown alongside papayas and bananas in villagers’ backyards, and is a delightful treat during the hot days of summer – often blended with sugar syrup as refreshing drinks. When eaten as it is, its sourness is obvious. Locals look for the fruit whenever they suffer from mouth ulcers. Very soft when ripe, the green skin is easily pinched and peeled away by hand, or sliced with a knife to reveal its aromatic, pulpy and juicy flesh. Enjoying soursop with your hands can be a messy undertaking, best slice open and dig in with a knife and fork, while discarding the small and oval black seeds. A distant cousin to the soursop that you may also find widely sold in Bali’s fruit markets, such as Badung and Kumbasari in Denpasar, is the custard apple, locally known as ‘silik’. Smaller and rounder, the size of an apple, the flesh is similarly tender, but tastes much sweeter.

  
  

  
  
  
  
  
  
  

  Java Plum

  
  

  Juwet
  Similar to the buah buni, the Java Plum is a seasonal fruit, widely grown in the southern Bukit region, and sold in warungs and roadside stalls, and alternatively prepared with a chilli mix. The fruit grows on large trees with dense foliage, and are smooth and shiny, oval-shaped the size of a date. Young green fruit turn pink and then purplish to black when ripe. The taste ranges from sweet to sour. Part of the fun in enjoying Java Plum is, after some bites and chews, you can check your tongue in a mirror – it will be slightly purple. The taste will also linger in your mouth for a while after enjoying even just a little amount. This is perhaps one of the reasons the locals tend to enjoy anything originally sweet and sour with the typical ‘rujak’ mix of shrimp paste, salt, sugar and chilli. You can always ask for a reduction or total omission of the slightly intimidating last ingredient.

  
  

  
  
  
  
  
  
  

  Yellow and Orange Coconut

  
  

  Nyuh Gading
  A widespread but often overlooked fruit: This is not the common green coconut. In Bali, the orange and yellow types are grown for their use in temple and ceremonial purposes. On the culinary side, while much smaller than the common green coconut, the young coconuts of the orange variety offer a much tastier and refreshing treat – the flesh is thinner and tender, and its water is more flavoursome. While not widely sold in tourist areas, you can find them in villages and rural areas where roadside stalls selling flowers usually sell them for ceremonial purposes. If you find a tree bearing these orange coconuts grown in your hotel’s grounds, kindly ask the staff if you can try one. Some hotels in Lovina, North Bali, such as the Puri Saron Baruna Beach Cottage, promote local fruits growing on their property’s premises, which can be a fun experience.

  
  

  
  
  
  
  
  
  

  Ambarella

  
  

  Kedondong
  This tropical fruit grows on low trees, and is green to a lighter colour when ripe. Its flesh is crunchy and a little sour, and is high in vitamin C. Again, it is one of the favourite naturally sour fruits that go with shrimp paste; a sugar, salt and chilli mix, forming a basic ‘rujak kedondong’. The fruit can also be pickled. Preferably peeled and sliced before eaten raw, ambarella contains a spiny seed that you should avoid getting in between your teeth. Warungs (traditional roadside snack stalls) selling rujak will almost always have ambarella among their stock of fruits. Widely available in traditional markets and supermarkets, the locals believe that eating ambarella improves the digestive system and can help cure anaemia.

  
  

  
  
  
  
  
  
  

  Pomelo

  
  

  Jeruk Bali
  A backyard-grown fruit that is also widely sold in traditional markets and supermarkets, this large citrus fruit comes in two general types based on the colour of the flesh, namely white and pink. The rind is thick and spongy, and getting out the lobes in one piece can be a challenge as the small pulps are brittle and break off easily. It is quite juicy after you crunch a mouthful of the pulp, and tastes sweet and sometimes bitter (usually the trait of the pink fleshed varieties). A local belief is that consuming pomelo can cure a hangover. The thick and spongy rinds shouldn’t be wasted – they are burnt to act as a natural mosquito repellent.

 

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 ////////

Fragmentation in mass spectrometry

Fragmentation

When molecules go through a mass spectrometer, some of them arrive intact at the detector, but many of them break into pieces in a variety of different ways. To establish a charge on a molecule, an electron had to be removed; removal of that electron is effected through a collision, usually with a high-energy electron. During that collision, energy is transferred from the high-energy electron to the molecule, and that energy has to go somewhere. Part of it gets partitioned into various bond vibrations, so bonds start to vibrate quite a lot, until some of them snap completely. The molecular ion breaks apart and forms a fragment ion.

Some fragment ions are very common in mass spectrometry. These ions are seen frequently for either of two reasons:

• there is not a pathway available to break the ion down.
• the ion is relatively stable, so it forms easily.

Fragmentations occur through well-defined pathways or mechanisms. A mechanism is a step-by-step series of events that happens in a reaction. It is important to understand how reactions happen, but we will look at fragmentations when we study radical reactions.

However, it is useful to know what factors make cations stable.

Some Common Ions

There are a number of ions commonly seen in mass spectrometry that tell you a little bit about the structure. Just like with anions, there are a couple of common factors influence cation stability:

• Electronegativity plays a role. More electronegative atoms are less likely to be cations.
• Polarizability also plays a role. More polarizable atoms are more likely to be cations.

However, in most cases, we will be looking at carbon with a positive charge, and there are additional factors to distinguish between them

• Delocalization stabilizes a cation by spreading out the charge onto two or more different atoms.
• In Lewis structure terms, the easiest way to delocalize charge is via resonance.
• Resonance can involve other carbons, like in allyl and benzyl cations.

• Resonance can also involve other atoms, like in acylium or iminium cations.

• Delocalization can also be accomplished through inductive effects. The trend in carbocations is that the more substituents on teh carbocation, the greater the stability.
• Tertiary cations, with three substituents on the carbocation, are more stable than secondary cations, with two substituents on the carbocation. Secondary cations are more stable than primary ones. Primary cations are more stable than methyl cations.

Molecular orbital calculations suggest that the cation is stabilized through interaction with neighboring C-H bonds in the alkyl groups. Specifically, a C-H sigma bonding orbital has symmetry similar to the empty p orbital on the positive carbon. The lobes on the two orbitals can overlap such that they are in phase, and that allows electrons to be donated from the C-H bond to the central, electron-deficient carbon. Formally, there is a bonding interaction and an antibonding interaction between these two orbitals. Since one of these orbitals is empty, the antibonding combination remains unoccupied. The bonding combination is populated, however, and since it is lower in energy than either the p orbital or the C-H sigma bond (all bonding combinations are lower in energy than the orbitals that combine to form them), there is a net decrease in energy.



 Fragmentation Patterns
The fragmentation of molecular ions into an assortment of fragment ions is a mixed blessing. The nature of the fragments often provides a clue to the molecular structure, but if the molecular ion has a lifetime of less than a few microseconds it will not survive long enough to be observed. Without a molecular ion peak as a reference, the difficulty of interpreting a mass spectrum increases markedly. Fortunately, most organic compounds give mass spectra that include a molecular ion, and those that do not often respond successfully to the use of milder ionization conditions. Among simple organic compounds, the most stable molecular ions are those from aromatic rings, other conjugated pi-electron systems and cycloalkanes. Alcohols, ethers and highly branched alkanes generally show the greatest tendency toward fragmentation.

The mass spectrum of dodecane on the right illustrates the behavior of an unbranched alkane. Since there are no heteroatoms in this molecule, there are no non-bonding valence shell electrons. Consequently, the radical cation character of the molecular ion (m/z = 170) is delocalized over all the covalent bonds. Fragmentation of C-C bonds occurs because they are usually weaker than C-H bonds, and this produces a mixture of alkyl radicals and alkyl carbocations. The positive charge commonly resides on the smaller fragment, so we see a homologous series of hexyl (m/z = 85), pentyl (m/z = 71), butyl (m/z = 57), propyl (m/z = 43), ethyl (m/z = 29) and methyl (m/z = 15) cations. These are accompanied by a set of corresponding alkenyl carbocations (e.g. m/z = 55, 41 &27) formed by loss of 2 H. All of the significant fragment ions in this spectrum are even-electron ions. In most alkane spectra the propyl and butyl ions are the most abundant.
The presence of a functional group, particularly one having a heteroatom Y with non-bonding valence electrons (Y = N, O, S, X etc.), can dramatically alter the fragmentation pattern of a compound. This influence is thought to occur because of a "localization" of the radical cation component of the molecular ion on the heteroatom. After all, it is easier to remove (ionize) a non-bonding electron than one that is part of a covalent bond. By localizing the reactive moiety, certain fragmentation processes will be favored. These are summarized in the following diagram, where the green shaded box at the top displays examples of such "localized" molecular ions. The first two fragmentation paths lead to even-electron ions, and the elimination (path #3) gives an odd-electron ion. Note the use of different curved arrows to show single electron shifts compared with electron pair shifts.

The charge distributions shown above are common, but for each cleavage process the charge may sometimes be carried by the other (neutral) species, and both fragment ions are observed. Of the three cleavage reactions described here, the alpha-cleavage is generally favored for nitrogen, oxygen and sulfur compounds. Indeed, in the previously displayed spectra of 4-methyl-3-pentene-2-one and N,N-diethylmethylamine the major fragment ions come from alpha-cleavages. Further examples of functional group influence on fragmentation are provided by a selection of compounds that may be examined by clicking the left button below. Useful tables of common fragment ions and neutral species may be viewed by clicking the right button.
The complexity of fragmentation patterns has led to mass spectra being used as "fingerprints" for identifying compounds. Environmental pollutants, pesticide residues on food, and controlled substance identification are but a few examples of this application. Extremely small samples of an unknown substance (a microgram or less) are sufficient for such analysis. The following mass spectrum of cocaine demonstrates how a forensic laboratory might determine the nature of an unknown street drug. Even though extensive fragmentation has occurred, many of the more abundant ions (identified by magenta numbers) can be rationalized by the three mechanisms shown above. Plausible assignments may be seen by clicking on the spectrum, and it should be noted that all are even-electron ions. The m/z = 42 ion might be any or all of the following: C₃H₆, C₂H₂O or C₂H₄N. A precise assignment could be made from a high-resolution m/z value (next section).

Odd-electron fragment ions are often formed by characteristic rearrangements in which stable neutral fragments are lost. Mechanisms for some of these rearrangements have been identified by following the course of isotopically labeled molecular ions.

Isotopes: 13C

Isotopomers or isotopic isomers are isomers with isotopic atoms, having the same number of each isotope of each element but differing in their positions.

Isotopomers

If you look closely at the mass spectrum of an organic compound, 2-butanone, you see a line at m/z 72, which corresponds to 4 carbons, an oxygen and 8 hydrogens.

Figure MS3. Mass spectrum of 2-butanone.

Source: SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology of Japan, 22 August 2008)

• Usually, whole numbers are used for molecular weights in mass spectrometry.
• The atomic masses in the periodic table, out to 4 decimal places, are the average masses including different possible isotopes.
• Because mass spectrometry examines individual molecules, individual atomic masses are needed, not average ones. Usually that means using a whole number.

In addition, there are a number of other lines at lower values of m/z; these correspond to the masses of smaller pieces of those 2-butanone molecules that fall apart during the experiment. We won't look too closely at how those arise until we get to radical reactions later in the course. However, we will look at some factors that make cations stable later in this chapter.

If you look closely at the mass spectrum of 2-butanone, you'll also see another little peak at m/z 73. This is referred to as the M+1 peak (one greater than the molecular ion), and it arises because of ¹³C. This compound is referred to as an isotopomer; that means the same compound with a different isotope.

• ¹²C is about 99% abundant; 99% of carbon atoms have a mass of 12 amu.
• ¹³C is about 1% abundant; 1% of carbon atoms have a mass of 13 amu.
• Compounds that contain a ¹³C atom have a mass one larger than expected.

The chance that a molecule in a sample contains a ¹³C atom is related to the number of carbons present. If there is just one carbon atom in the molecule, it has a 1% chance of being a ¹³C. That means the M+1 peak would be only 1/100th as tall as M+, the peak for the molecular ion.

• The M+1 peak from a ¹³C atom is very small.
• The more carbons there are in a molecule, the bigger the M+1 peak.
• If there are 10 carbon atoms in the molecule, there is a 10% chance of a ¹³C atom being present. The M+1 peak is about 1/10th the size of the M+ peak.
• If there are 100 carbons in the molecule, there is a very good chance that a ¹³C atom is present. At that point, the M+1 peak is actually much larger than the M+. peak