Rf values in TLC

Preparation of 17-cyclopropylmethyl-14-hydroxynorcodeinone. A solution of 17-cyclopropylmethylnorcodeinone (0.20 g, 0.59 mmol), formic acid (90%, 0.304 g), water (0.504 g), EtOAc (0.27 g), and hydrogen peroxide (30%, 0.17 g) was heated at 42°-43°C for 15 hr, added water (20 ml), basified with Na2C03 (1.02g), and extracted with EtOAc (80 ml and 2 times 20 ml). The combined extract was washed with water, dried over anhydrous sodium sulfate, and evaporated in vacuo to dryness to give 17-cyclopropylmethyl-14-hydroxynorcodeinone (0.10 g, 56% yield). The Rf value in TLC and the IR spectrum of the product were comparable to those obtained from an authentic sample. 

Fig. 3. Separation of Tabernaemontana alkaloids by means of droplet counter current chromatography compared to a thin-layer chromatograhic separation, y-axis Rf value in TLC system CHCl3-MeOH (9 1) on silica plates X-axis separation in DCCC-system (Table 6).

Only Letham and Miller [68 a, 69] appear to have used TLC so far. They compared the zeatin obtained from immature fruit of Zea mays with the maize factor , isolated likewise from maize grains. The preparations, characterised through their kinetin activity, are evidently identical. They accordingly show the same Rf-values in TLC on alumina G with butanone, saturated with water (hRf 58) with ethyl acetate saturated with water IciRf 14) and with chloroform-95% ethanol (10 4- 90, hRf 86, 90 + 10, hRf 61). The compound is 6-(4-hydroxy-3-methylbut-trans-2-Giiy ) aminopurine. 

In C.halimii leaf wax triterpenoids were found in the very high amount of 72%,beside the wax lipids. The free triterpenols dominated with about 62%. Identified could be B-amyrin, a-amyrin and lupeol. In small amounts esters of B-amyrin and a-amyrin containing long chain fatty acids were found. Again triterpene ketones were isolated and detected with the aid of GC/MS. In this wax lupenone was present and also one other ketone named fridelanone in the remarkable amount of about 12%. They could be reduced to the corresponding alcohols. Fridelanone and fride-lanol have a pentacyclic structure without any double bond. Therefore these substances showed quite different Rf values in TLC and no colour reaction with carbazole (3)(Fig.l). 

Having proven the purity of each pigment, the next stage is to study its physicochemical characteristics. The typical coloration shown by these compounds in TLC under white and UV254 m fight, and the corresponding Rf values in TLC—in both normal and reversed phase—are the first guiding data in their characterization. Subsequently, absorption spectra are obtained in different solvents, whose dielectric... 

Interpreting a GC is about the same as interpreting a TLC plate, so I ll use TLC terms as comparison to show the similarities. Remember the Rf value from TLC The ratio of the distance the eluent moved to how far the spots of compound moved Well, distances can be related to times, so the equivalent of Rf in GC is retention time. It s the time it takes the sample to move... 

Figure 5.6—Example of interdependency of R/ values on resolution in an HPLC column. It is possible to transpose results obtained by TLC onto HPLC using the same phases. Resolution between two compounds on a TLC plate varies with the distance of migration on the plate. Resolution passes through a maximum for an Rf value in the order of 0.3.

Thy-l glycolipids had different TLC Rf values in solvent 1 and solvent 2. The mobility of brain Thy-l glycolipids was very similar to Gq3 ganglioside in that they migrated ahead of Gjji in solvent 2, and behind G i and slightly ahead of GDla in solvent... 

It is worth noting, that diastereomeric hemicarceplexes synthesized from the (5,5)-26b and racemic 2-butanol (in ratio 4 1) show quite different Rf values on TLC [0.8 for the major product and 0.5 for the minor one, eluant CHCl3-EtOAc 20 1 (v/v)]. Thus, even incarcerated chiral molecules provide different sorption properties that are transferred through the thick shelf of hemicarceplexes to the outside. 

The difference in the rate constants for guest release from (5)-27a leads to AAG = 2.3 and 1.9 kcal mol-1 for 1,2-dibromopropane and 1,2-dichloropropane, respectively. Again, the diastereomeric complexes of (5)-27a and (5,5)-27b with phenyl methyl sulfoxide gave quite different RF values on TLC (eluent CH2C12, 2% EtOAc). 

Compound 52 an effective anti-hypertensive drug, has been synthesized44b for biotransformation studies from p-chlorobenzoic acid-carbonyl-14C (53) in three steps modifying the methods of Sturm45, Hoefle46 and coworkers (equation 23). The intermediate 4-chloro-3-sulphamoylbenzoic acid-carbonyl-14C (54) with thionyl chloride yielded the acid chloride 55, which with 2-amino-3aa, 4a,5,6,7aa-hexahydro-4,7-methano-isoindoline gave the carbonyl-14C labelled compound 52. The UV spectra of 52 and of the unlabelled 52 as well as the Rf value on TLC of the single radioactive peak and of the fluorescent spot of unlabelled authentic specimen of 52 coincided. 

Previous workers who have reported Rf values for TLC systems have generally ignored the importance of all six of the above experimental elTects. Consequently, these data are of limited value for the development of a quantitative theory of adsorption chromatography. However, rigorous attention to all these effects in TLC would undoubtedly result in procedures which are much more time consuming than are corresponding measurements by column elution (b). Consequently, column elution appears more suitable for obtaining accurate AT values at the present time. 

Evaporation of the xylene filtrate and trituration of the residue with methylene chloride yields ca. 11 g of solid which consists mainly of cyclic hexamer and cyclic tetramer. The methylene chloride contains inter alia, cyclic pentamer, cyclic heptamer, and bishomo compound, and these can be obtained as pure samples in low yield by fractional crystallization procedures. The compositon of the reaction mixtures can be qualitatively established by TLC by means of the following Rf values in 9 1 petroleum... 

The selectivity of TLC systems was compared by use of correlations between Rf(ll) and Rf(l) (by analogy with two-dimensional TLC). The greatest spread of points, indicative of individual selectivity, was obtained for nonaqueous mobile phases on silica and aqueous mobile phases on octadecyl silica adsorbent wettable with water (RP-18 W). The correlation of Rf values in normal- and reversed-phase systems was utilized in the practical separation of a mixture of 14 triazines and urea herbicides using 2-D TLC on a Multi-K CSS dual phase (3 cm strip of octadecyl silica parallel to silica layer). The plate was videoscanned showing the real picture of the plate <2002JCH277>. 

The location of the hydroxy substituent in compounds like juglone and 7-methyljuglone (Fig. 18) influences the retention of these compounds. Intramolecular hydrogen bonding between the keto group and the hydroxyl substituent reduces the polarity and results in relatively high Rf values. In contrast, lawsone (Fig. 18) is strongly sorbed on the TLC layer. 

It should be noted that to obtain the best results in any of these quantitative TLC methods, the spots being used should have Rf values between 0.3 and 0.7 spots with R( values <0.3 tend to be too concentrated whereas those with Rf values >0.7 are too diffuse. 

TLC analysis of the crude product (elution with 50 1 pentane ether, visualization with iodine) showed three non-baseline spots Rf 0.65 (cis isomer), Rf 0.52 (unknown impurity), and Rf 0.32 (trans isomer). The unknown impurity is intensely sensitive to iodine and largely coelutes with the cw-isomer in the subsequent column chromatography. However, the ll NMR spectrum of this isomer shows excellent purity despite the presence of this spot on TLC. In 100 1 pentane ether, Rf values of the cis and trans isomers are about 0.50 and 0.15, respectively. 

To ascertain that aminomethylphosphonic acid ( ) but not glycine (4) is a photolysis product, the primary amino product was identified by comparison of TLC Rf values. Possible products and their formation pathways from photolytic cleavage of N-nitrosoglyphosate are shown in Figure 1 (5). The TLC Rf values on silica gel for different solvent systems are shown in Table II (5). The data clearly indicate that aminomethylphosphonic acid... 

The mobile phase is usually seleeted by trial-and-error guided by prior experience or by performing preliminary analytieal separations of the sample in a saturated ehamber. PLC separations will be inferior to analytical TLC separations using the same mobile phase beeause of the thieker layer, larger particle size, and overloaded sample eonditions used for PLC. A good general rule is that analytical TLC should achieve separations with least 0.1 Rf value difference if the PLC separations are to be adequate with the transferred mobile phase. Isocratic development is usually used, but gradient development has been applied in certain situations for increased resolution. 

These chromatographic performance tests are carried out in order to ensure that all impurities to be controlled are well separated from the substance to be examined (HPLC, GC andTLC). Forthis reason, preferably such reference substances are chosen which elute dose to the main compoxmd (HPLC, GC) or which have a similar Rf-value (TLC) but can stiU be separated. These may be structurally related compoimds which shall be separated with a minimum requirement for the resolution using the chromatographic system described, e.g. such as in the monograph for desmopressin (Monograph 07121999), Figure 5.3. 

The fundamental parimeter used to characterize the position of a saaple zone in a TLC chromatograa is the retardation factor, or Rf value. It represents the ratio of the distance migrated by the saaple compared to that traveled by the solvent front. With respect to Figure 7.1, the Rf value for linear development is given by equation (7.1)... 

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