The preparation of novel fluorinated poly(β-hydroxyalkanoates), PHAs, was carried out using Pseudomonas oleovorans (ATCC 29347) and Pseudomonas putida (KT 2442) as biocatalysts. These organisms were first grown on 40 mM sodium citrate prior to studying polymer formation in the second stage using 1:1 molar mixtures of nonanoic acid (NA) and fluorinated acid cosubstrates. The following fluoro acids were synthesized and used in this study:  6,6,6-trifluorohexanoic acid (TFHxA), 6,6,7,7,8,8,8-heptafluorooctanoic acid (HpFOA), 6,6,7,7,8,8,9,9,9-nonafluorononanoic acid (NFNA), and 6,6,7,7,8,8,9,9,10,10,11,11,11-tridecafluoroundecanoic acid (TDFUDA). In general, the use of NA/fluoro acid cosubstrate mixtures instead of only NA in second-stage cultivations resulted in little to no cellular toxicity as measured by values of colony-forming units per milliliter. The mol percent incorporations of fluorinated side chains was determined by 1H and 19F NMR spectroscopies, and peak assignments were made using two-dimensional reverse-detected heteronuclear multiplet quantum correlation (HMQC) as well as 1H−H correlation spectroscopy (COSY). P. putida formed PHA after a 3-day second-stage cultivation time with 17.3 mol % fluorinated side chains using NA/NFNA as cosubstrates. For shorter second-stage cultivation times (1 day) where product yields were relatively higher, 0.3 g/L of product was formed that contained 6.4 mol % fluoroalkanoate side groups using P. oleovorans as the biocatalyst and NA/HpFOA as cosubstrates. The incorporation of 12.4 mol % fluoroalkanoate repeat units resulted in products which showed melting at higher temperatures (55−80 °C), crystallized at faster rates from the melt, and had higher heats of fusion. Investigation of the surface free energy of products by surface contact angle measurements showed only a modest increase from 87 to 94° for PHAs containing 0 and 17.3 mol % fluorinated side chains.

Solvolysis as a Steric PhenomenonSir : We wish to report that in three representative Ushaped systems examined, cis-bicyclo[3.3.0]octane, norbornane, and endo-5,6-trimethylenenorbornane, noncarbonium ion reactions exhibit preferences for reaction at the exo face that are comparable in magnitude to the exo:endo rate ratios observed in the solvolyses of the tertiary methyl p-nitrobenzoates. This common pattern of reactivity suggests that steric factors must contribute to the greater reactivity from the exo direction exhibited by all reactions, carbonium ion as well as noncarbonium ion.It is well known thst exo-norbornyl derivatives undergo solvolysis at rates that are considerably greater than those of the corresponding endo isomers. Moreover, the resulting ion or ion pair undergoes substitution to give the exo isomer predominantly. This preference for exo reactivity and exo attack has been attributed to a participation leading to the formation of a a-bridged cation.'It has become evident in recent years that this exo preference is not restricted to carbonium ion reactions. Many reactions not involving carbonium ions exhibit a similar preference for exo attack, although the magnitude of the effect may vary considerably from reaction to rea~tion.~,3 With data now available for the solvolysis of the tertiary methylp-nitrobenzoates of the cisbicyclo[3.3.0]octane4 (X), norbornane5 (XI), and endo-5,6-trirnethylenenorb~rnane~ (XII) systems, we decided to examine a number of typical reactions of these systems in order to ascertain whether the parallelism previously noted for norbornane extends to these additional U-shaped structures.OPNB the 4-5 bond is in a very poor position geometrically to participate. Participation would involve resonance with a very highly strained tetracyclic cation. No rearrangements to this tetracyclic structure are observed in the solvolysis of the tertiary (Table 11) or the secondary derivatives, The high exo : endo ratio arises not as a result of any very high rate for the exo isomer, compared to I, but because of a greatly reduced rate for the endo. Table 11. Products in the Solvolysis of VIII-OPNB ~ VIII-X-OPNB 100 0%. 24% 22% 51% VIII-N-OPNB 125 1 % 19% 19% 44% a <0.2%, the limit of detectability.It follows that the exo:endo rate ratio of 4300 for the VIII and of 19 for the I X derivatives must be primarily steric in origin.It should be noted that VIII-X-OPNB and IX-X-OPNB exhibit rates that are very similar to that of I. This may be fortuitous. It was pointed out earlier that decreased flexibility in the ring might be expected to result in a moderate decrease in rate.6 Possibly relief of steric strain, engendered by the rotation of the methyl group out of the crowded endo environment, provides a driving force that compensates for the anticipated effect of reduced flexibility.It follows from the similarity in the steric requirements of the methyl and acyloxy groups' that the same strains must be present in the endo isomers. The slow rate of the endo isomers can onIy mean that, in contrast...

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The exo:endo rate ratios for the solvolysis in 80% acetone at 25 °C of the p-nitrobenzoates of tertiary bicyclic alcohols of widely varying U-shape character, such as 2-methyl-and 3-methyl-cis-bicyclo[3.3.0]octanols, 2methyl-2-norbornanol, and 2-, 8-, and 9-methyl-endo-5,6-trimethylene-2-, -8-, and -9-norbornanols increase with increasing U-shape character of the bicyclic skeleton. This supports the proposal that steric retardation of ionization of the endo isomer is a major factor in governing the exo:endo rate ratios in these tertiary systems. A comparison of the solvolysis data with those of representative nonsolvolytic reactions in these U-shaped systems indicates that the exo/endo relative reactivities reveal a similar pattern for all of the reactions. The exo:endo ratios (product or rate) increase with increasing U-shape character of the bicyclic skeleton. Thus the large exo:endo rate ratio in the solvolysis of tertiary 2-norbornyl derivatives may as well be due to steric rather than to the long proposed