Piano analogy

Today musicians take for granted that their instruments are polyphonic. Early analog instruments were monophonic, that is, they only could produce one note a time like a clarinet, which can only produce one note at a time. Musicians used to pianos expected to have arbitrary polyphony available since with a piano, a player could conceivably press up to all 88 keys simultaneously. 

In a few cases, the stereochemistry of adducts has been elucidated from their vibrational and NMR spectra. The arrangement in compound (IV) has already been displayed, the product of the reaction in entry 30 is known to be (V) (223) [and this is confirmed by an X-ray study of the GeMe3 analog (202)], while the product in entry 33 is (VI) (229). The adduct Ph3SiMnH(CO)2(Cp) (entry 4) adopts a piano-stool... 

The reaction of (OEP)ZrCl2 with 3equiv. of LiC=CPh produces the alkynyl (OEP)Zr(lv) porphyrin complex (OEP)Zr(7]1-C=CPh)3Li(THF) 242194 (Equation (18)). The molecular structure shows that three alkynyl ligands are coordinated to the Zr center in a piano-stool fashion and that the lithium cation is bound to the pocket formed by three alkynyl ligands. Treatment of complex 242 with anhydrous HC1 produces a C-C bond-coupled product H2C=C(Ph)=CPh and HC=CPh quantitatively. This example shows different reactivity of the zirconium porphyrin from that of analogous metallocene complexes. 

The frequency of a noise is analogous to its tonal quality or pitch. The fundamental frequency of middle C on a piano keyboard, for example, is 262 Hz. A tuning fork produces sound at a single frequency, often called a discrete tone. Transformers prodnce sonnd at several discrete freqnencies that are even multiples of hne frequency. In the United States, transformer noise is concentrated at 120,240,360,480, and 600 Hz. However, most sounds include a composite of many frequencies and are characterized as random or broadband. Rotating equipment such as fans and motors usually produces both broadband and discrete tonal noise. 

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