Difficult consonants

Now we turn to some more problematic cases. In English, the consonants /dh/, /zh/, /ng/ and /h/ are a little more difficult to deal with. There are clearly exactly four unvoiced fricatives /th/, /f/, /s/ and /sh/ in English and of these, /f/ and /s/ have the voiced equivalents /v/ and /z/, and these are unproblematic. The voiced equivalent of /th/ is /dh/ and while /th/ is a common enough phoneme, /dh/ only occurs in very particular patterns. For a start, the number of minimal pairs that occur between /dh/ and /th/ are few real examples include teeth noun, /1 iy th/ and teeth.verb, /t iy dh/, while most are near minimal pairs such as bath /b ae th/ and bathe / b ey dh/ where the quality of the vowel differs. Even if we except /dh/ as a phoneme on this basis, it occurs in strange lexicon patterns. In an analysis of one dictionary, it occurred in only about 100 words out of a total of 25,000. But if we take token count into consideration, we find in fact that it is one of the most common phonemes of all in that it occurs in some of the most common function words 

The sounds [ng] and [h] are noteworthy because they are severely restricted as to the positions they can occur in. Primarily, hl can not occur at the end of a syllable or a word, and /ng/ can not occur at the beginning of a syllable or word. There are further issues with /ng/ in that as it only occurs in a post-vocalic position, it suffers from the loss of contrast that affects all nasals in this position. So while it is clear that sin, / s ih n/, siM, /s ih m/ and sing, /s ih ng/ all end in different sounds, it is less clear what the eorrect representation for words like think should be. In words such as this the last stop is in a velar position, and the nasal takes on a velar qualify also (this is similar to the ten boys effeet we discussed earlier). The issue is then whether we should use a velar nasal /ng/ or a dental nasal /n/ there is no contrast possible in this position and so it is a question of convention which we should pick. As with other sueh issues, the main goal is to aim for consistency if /ng/ is used here then it should be used in all other post-vocalic pre-velar stop positions. 

Now we turn to some more problematic cases. In English, the consonants /dh/, /zh/, /ng/ and /h/ are a little more difficult to deal with. There are clearly exactly fom imvoiced fricatives /th/, /f/, /s/ and /sh/ in Enghsh and, of these, /f/ and /s/ have the voiced equivalents /v/ and /z/, which are unproblematic. The voiced equivalent of /th/ is /dh/ and. 

---

In the retrosynthetic direction, consonant relationships must be disconnected, in principle, before the dissonant ones (this means that in the actual synthesis the more difficult reactions leading to dissonant relationships must be attacked in the first place. It is always less painful to deal with failures in the first stages of a synthesis). 

The order of redox potentials for oxidation of (4) (F>C1 Br) has been reported and found most consistent with a detectable resonance contribution through the a-framework. The most difficult oxidation of (5) (despite the fluoro substituent being one carbon atom more removed from the double bond) is consistent with the Whiffer effect (cr-hyperconjugative destabilization proceeding through two pathways is more than double tiie same effect through one pathway), in consonance with the AMI prediction. The facial selectivity of epoxidation and diazetidme formation from (4) proved to be hi... 

There are several terms you should be familiar with for voltaic cells. First, the voltage that is impressed across the circuit (that is, the difference in electrical potential between the zinc strip and the copper strip) is known as the cell voltage, which is also occasionally called the cell potential or the electromotive force, EMF. The copper electrode, because it becomes negatively charged and attracts cations, is known as the cathode. The zinc electrode becomes positively charged and is known as the anode. You are expected to know which part of the reaction takes place at the cathode and which part takes place at the anode. These can sometimes be difficult to remember, so a simple mnemonic device can help you distinguish between the two. Oxidation occurs at the Anode (note how each term starts with a vowel), and deduction occurs at the Cathode (note how each term starts with a consonant). 

Finally the introduction of cyclopropane or vinylcyclopropane into organic compounds provides an opportunity to cross the odd/even manifolds in further synthetic steps aimed at the preparation of compounds of increased molecular complexity. Traditionally, any synthesis that involves intermediates with an odd number of atoms is more difficult because proper charge parity or consonance cannot be observed. A cyclopropane unit then functions as a topological operator in those cases where such crossover is desired. ... 

With that said, there are a few tricks to increasing the odds that your paper cut will work. It s generally easier to cut into a hard consonant, such as b, t, or v. Words that begin with soft consonants, such as s or h, can be more difficult. Note that just because you cut the "Well" from "Well, I think it started" doesn t mean that the editor can make the excision. Usually, though, if one bite or cut doesn t work, there will be something else available that s close enough. 

An alternative is to define a completely different set of symbols. A common approach in speech technology is to use one or more ascii characters for each phoneme, so that the consonant at the start of shoe is /sh/, the vowel is /uw/ and so on. Note that the use of ascii characters is relatively easy when our task is to represent 50 or less phonemes coming up with a unique ascii representation for each hundreds phones is much more difficult. For now we will use the modified limit ascii character set, defined for general American English a full description and justification of this will be given in Chapter 8. In addition to any practical, computer benefit, the use of a... 

---