Carbon propene

The chemical reactivity of these two substituted ethenes is in agreement with the MO and resonance descriptions. Amino-substituted alkenes, known as enamines, are very reactive toward electrophilic species and it is the 6-carbon that is the site of attack. For example, enamines are protonated on the 6-carbon. Propenal is an electrophilic alkene, as predicted, and the nucleophile attacks the 6-carbon. 

Hydro- carbon Propene Propane Butane Ethane Propene Propene Propene Propane Propene Ethylene Ethylene... 

When trying to estimate the hydrocarbon family from the molecular formula, there is a ratio that indicates the alkenes. With the aUcene family, there are twice as many hydrogen atoms as carbons. Propene has three carbons 3 x 2 = 6, so there are three carbon atoms and six hydrogen atoms in propene (CjHg). In the case of alkenes that have more than one double bond, the ratio does not work. It is better to look at a molecular formula and draw out the structure rather than to try to guess from the ratio of the molecular formula. While the ratios work most of the time, there are exceptions, such as the two and three double-bonded compounds. 

Almost any hydrocarbon can serve as a starting material for production of ethylene and propene Cracking of petroleum (Section 2 16) gives ethylene and propene by processes involving cleavage of carbon-carbon bonds of higher molecular weight hydrocarbons... 

There are two different types of carbon-carbon bonds m propene CH3CH=CH2 The double bond is of the ct + tt type and the bond to the methyl group is a ct bond formed by sp -sp overlap... 

The general molecular formula for an alkene is Cr,H2n Ethylene is C2H4 propene IS C3H6 Counting the carbons and hydrogens of the compound shown (CsHie) reveals that it too corresponds to CnH2n... 

Although ethylene is the only two carbon alkene and propene the only three carbon alkene there are four isomeric alkenes of molecular formula C4Hj ... 

Cis-trans stereoisomerism m alkenes is not possible when one of the doubly bonded carbons bears two identical substituents Thus neither 1 butene nor 2 methyl propene can have stereoisomers... 

Athene formation requires that X and Y be substituents on adjacent carbon atoms By mak mg X the reference atom and identifying the carbon attached to it as the a carbon we see that atom Y is a substituent on the p carbon Carbons succeedmgly more remote from the reference atom are designated 7 8 and so on Only p elimination reactions will be dis cussed m this chapter [Beta (p) elimination reactions are also known as i 2 eliminations ] You are already familiar with one type of p elimination having seen m Section 5 1 that ethylene and propene are prepared on an industrial scale by the high temperature dehydrogenation of ethane and propane Both reactions involve (3 elimination of H2... 

FIGURE 7 16 Poly mers of propene The mam chain IS shown in a zigzag conformation Every other carbon bears a methyl sub stituent and is a chirality center (a) All the methyl groups are on the same side of the carbon chain in isotactic polypropylene (b) Methyl groups alternate from one side to the other in syndiotactic polypropy lene (c) The spatial orienta tion of the methyl groups IS random in atactic polypropylene... 

The pattern is repeated m higher alkynes as shown when comparing propyne and propene The bonds to the sp hybridized carbons of propyne are shorter than the corre spondmg bonds to the sp hybridized carbons of propene... 

At 146 pm the C 2—C 3 distance m 1 3 butadiene is relatively short for a carbon-carbon single bond This is most reasonably seen as a hybridization effect In ethane both carbons are sp hybridized and are separated by a distance of 153 pm The carbon-carbon single bond m propene unites sp and sp hybridized carbons and is shorter than that of ethane Both C 2 and C 3 are sp hybridized m 1 3 butadiene and a decrease m bond distance between them reflects the tendency of carbon to attract electrons more strongly as its s character increases... 

Methyl-2-propen-l-ol, purchased from Aldrich Chemical Company, was distilled from anhydrous potassium carbonate. It was added directly to the n-butyllithium solution using a long needle. The checkers quickly replaced the pressure-equalizing dropping funnel with a serum cap to carry out this addition. The funnel was fitted to a small dry flask to prevent the introduction of moisture during the addition period and replaced on the reaction flask immediately afterwards. 

The important hydrocarbon classes are alkanes, alkenes, aromatics, and oxygenates. The first three classes are generally released to the atmosphere, whereas the fourth class, the oxygenates, is generally formed in the atmosphere. Propene will be used to illustrate the types of reactions that take place with alkenes. Propene reactions are initiated by a chemical reaction of OH or O3 with the carbon-carbon double bond. The chemical steps that follow result in the formation of free radicals of several different types which can undergo reaction with O2, NO, SO2, and NO2 to promote the formation of photochemical smog products. 

Fig. 1.29. Interactions between two hydrogen Is orbitals and carbon 2p orbitals stabilize the eclipsed confonnation of propene.

The hydrofluonnation of alkenes also occurs in the gas phase, generally at somewhat higher temperatures [J]. Huoroethane is obtained m yields as high as 98% at 100 to 160 C by reaction in the presence of minor amounts of higher ot-olefms [6], and 2-fluoropropane is prepared in greater than 90% yield at <.80 "C from hydrogen fluonde and propene in the presence of activated carbon [7]... 

It s easy to identify the carbons involved in the double bond in ethylene atoms 1 and 2. In propene, things are slightly more complicated. In this case, the carbon which has three hydrogens attached to it is not involved in the double bond. We can identify this carbon atom as center number 3 by noting that it along with the final three hydrogen atoms all lie in the third quadrant (-X and -Y). Therefore the two carbons of interest are again atoms 1 and 2. 

By examining the positions of the atoms, we can determine what type of displacements would occur when the C=C bond stretches. The carbons in ethylene must both move in the Z direction, since they are situated on the Z-axis, while those in propene must move primarily in the X direction. 

In ethylene, both carbons have significant displacements in the Z direction (with opposite sign). In propene, their displacements are essentially in the X direction. In both cases, the hydrogens attached to these carbon atoms also move, as would be expected. 

Constructing a Z-matrix for propene provides a more challenging example. Note that the atoms inside the red line in the illustration all lie in a plane. First we ll specify the carbon atoms ... 

Dimethylborane+propene Cl depicts the transition state for addition of dimethylborane onto the terminal alkene carbon of propene. Examine and describe the vibration with the imaginary frequency. Which bonds stretch and compress the most What simultaneous changes in bonding are implied by these motions Simultaneously display the highest-occupied molecular orbital (HOMO) of propene and the lowest-unoccupied molecular orbital (LUMO) of dimethylborane. Is the overall geometry of the transition state consistent with constructive overlap between the two Explain. 

Examine the geometry and electrostatic potential map for acetone enolate. Are the CC and CO bonds in the enolate more similar to those in acetone or propen-2-ol precursors Is the negative charge primarily located on oxygen or on carbon Assuming this enolate is a hybrid of the two resonance contributors as shown above, which, if either, appears to be the major contributor ... 

Compare carbon-carbon bond distances in each diene. Which bond distances are unusually long or short Use propene as a model of a molecule with normal CC single and double bonds. Can resonance account for all of the unusual bond distances Is this the only explanation ... 

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