Triple bonds, hybrid orbitals

In triple-bond compounds (e.g., acetylene), carbon is connected to only two other atoms, and hence uses sp hybridization, which means that the four atoms are in a straight line (Fig. 1.6). Each carbon has two p orbitals remaining, with one electron in each. These orbitals are perpendicular to each other and to the C—C axis. They overlap in the manner shown in Figure 1.7 to form two n orbitals. A triple bond is thus composed of one a and two n orbitals. Triple bonds between carbon and nitrogen can be represented in a similar manner. 

Each atom has two effective pairs, which means that both are sp hybridized. The triple bond consists of a a bond produced by the overlap of an sp orbital from each atom and two tt bonds produced by the overlap of 2p orbitals from each atom. The lone pairs are in sp orbitals. Since the CO molecule has only two atoms, it must be linear. 

Each atom has two effective pairs, which means that both are sp hybridized. The triple bond consists of a cr bond produced by overlap of an sp orbital from each atom and... 

In acetylene, the carbon is sp hybridized. The triple bond is composed of one sigma bond, and two pi bonds. The bond angle is 180 . We should also realize that the sigma bonds are formed by sp hybrid orbitals, and the pi bonds are formed by the p orbitals. 

The aiTangement of hybrid orbitals is octahedral and the bond angles are 90°. 9.5B One of the 2s electrons in Be is promoted to an empty p orbital. The. 5 orbital and one p orbital hydridize to form two sp hybrid orbitals. Each hybrid orbital contains one electron and overlaps with a singly occupied 2p orbital on an F atom. The arrangement is linear with a bond angle of 180°. 9.6A 16 tr bonds and 4 tt bonds. 9.6B 17 rr bonds and 5 ir bonds. 9.7A C and N atoms are sp-hybridized. The triple bond between C and N is composed of one sigma bond (from overlap of hydrid orbitals) and two pi bonds (from interaction of remaining p orbitals). 

The NMR indicates that A is aromatic. The C s of the triple bond are sp hybridized. Each triple bond has one set of electrons in p orbitals that overlap with other p orbitals on A = adjacent atoms in the ring. This overlap allows electrons to... 

Section 2 21 Carbon is sp hybridized m acetylene and the triple bond is of the ct + Tt + Tt type The 2s orbital and one of the 2p orbitals combine to give two equivalent sp orbitals that have their axes m a straight line A ct bond between the two carbons is supplemented by two tr bonds formed by overlap of the remaining half filled p orbitals... 

Acetylene is linear and alkynes have a linear geometry of their X—C=C—Y units The carbon-carbon triple bond m alkynes is com posed of a CT and two tt components The triply bonded carbons are sp hybridized The ct component of the triple bond contains two electrons m an orbital generated by the overlap of sp hybndized orbitals on adja cent carbons Each of these carbons also has two 2p orbitals which over lap m parrs so as to give two tt orbitals each of which contains two electrons... 

When two sp-hybridized carbon atoms approach each other, sp hybrid orbitals on each carbon overlap head-on to form a strong sp-sp a bond. In addition, the pz orbitals from each carbon form a pz-pz it bond by sideways overlap and the py orbitals overlap similarly to form a py-py tt bond. The net effect is the sharing of six electrons and formation of a carbon-carbon triple bond. The two remaining sp hybrid orbitals each form a bond with hydrogen to complete the acetylene molecule (Figure 1.16). 

You might recall from Section 1.9 that a carbon-carbon triple bond results from the interaction of two sp-hybridized carbon atoms. The two sp hybrid orbitals of carbon lie at an angle of 180° to each other along an axis perpendicular to the axes of the two unhybridized 2py and 2pz orbitals. When two sp-hybridized carbons approach each other, one sp-sp a bond and two p-p -rr bonds are... 

In Section 7.2, we saw that insofar as geometry is concerned, a multiple bond acts as if it were a single bond. In other words, the extra electron pairs in a double or triple bond have no effect on the geometry of the molecule. This behavior is related to hybridization. The extra electron pairs in a multiple bond (one pair in a double bond, two pairs in a triple bond) are not located in hybrid orbitals. 

Now consider the alkynes, hydrocarbons with carbon-carbon triple bonds. The Lewis structure of the linear molecule ethyne (acetylene) is H—O C- H. To describe the bonding in a linear molecule, we need a hybridization scheme that produces two equivalent orbitals at 180° from each other this is sp hybridization. Each C atom has one electron in each of its two sp hybrid orbitals and one electron in each of its two perpendicular unhybridized 2p-orbitals (43). The electrons in the sp hybrid orbitals on the two carbon atoms pair and form a carbon—carbon tr-bond. The electrons in the remaining sp hybrid orbitals pair with hydrogen Ls-elec-trons to form two carbon—hydrogen o-bonds. The electrons in the two perpendicular sets of 2/z-orbitals pair with a side-by-side overlap, forming two ir-honds at 90° to each other. As in the N2 molecule, the electron density in the o-bonds forms a cylinder about the C—C bond axis. The resulting bonding pattern is shown in Fig. 3.23. 

Double and triple bonds, particularly those in carbon molecules, are often described in MO terms. Thus a double bond is described as consisting of a a bond formed by the overlap of an sp hybrid orbital on each carbon atom and a tt bond formed by the sideways overlap of either the 2p or 2p orbitals (Figure 3.18). A cr orbital has cylindrical symmetry like an atomic s orbital whereas a ir orbital, like an atomic p orbital, has a planar node passing through the nucleus of each of the bonded atoms. A triple bond is similarly described as consisting of a cr orbital and two ir orbitals formed from both the 2p and 2pv orbitals on... 

The left-most C atom (in the structure drawn below) is sp3 hybridized, and the C-H bonds to that C atom are between the sp3 orbitals on C and the Is orbital on H. The other two C atoms are sp hybridized. The right-hand C-H bond is between the sp orbital on C and the Is orbital on H. The c a C triple bond is composed of one sigma bond formed by overlap of sp orbitals, one from each C atom, and two pi bonds, each formed by the overlap of two 2p orbitals, one from each C atom (that is a 2py—2py overlap and a 2pz—2pz overlap). 

The third observation relates to acetylene (ethyne, C2H2), which is linear, i.e. bond angles of 180°, and contains two it bonds. This introduces what we term triple bonds, actually a combination of one a bond and two n bonds. In this molecule, we invoke another type of hybridization for carbon, that of sp hybrid orbitals. These are a mix of the 2s orbital with one 2p orbital, giving two equivalent sp orbitals. Each hybrid orbital takes one electron, whilst the remaining two electrons are accommodated in two different 2p orbitals (Figure 2.17). 

Bonding at two-valent carbon is linear, i.e. bond angles are 180°, and the triple bond comprises two jt bonds and a a single bond formed from sp hybrid orbitals (see Section 2.6.2). The two Jt bonds are at right angles to each other. 

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