Section A-Structure and bonding A5 SP HYBRIDIZATION Key Notes Definition In sp hybridization,the 2s orbital and one of the three 2p orbitals are'mixed' to form two hybridized sp orbitals of equal energy.Two 2p orbitals are left over and have slightly higher energy than the unhybridized orbitals. Electronic For carbon,each sp hybridized orbital contains a single unpaired electron. configuration There are also two half-filled 2p orbitals.Therefore,four bonds are possible. Geometry Each sp orbital is shaped like a deformed dumbbell with one lobe much larger than the other.The remaining 2p orbitals are symmetrical dumbbells. If we define the 2p orbitals as being aligned along the y and the z axes,the two sp hybridized orbitals point in opposite directions along thex axis. Alkynes bonds.Alkynes are linear molecules and are reactive due to the Nitrile groups The nitroge 个atrepea and carbon at9口ms一f a nitri1e93ae中 on has twe and can for bonds, the ca 2p orbitals which can be used to form twobonds Related topics Chemistry of nitriles(O4) Definition In sp hybridization,the 2s orbital is mixed with one of the 2p orbitals (e.g.2p,)to give two sp hybrid orbitals of equal energy.This leaves two 2p orbitals unaffected (2p,and 2p.)with slightly higher energy than the hybridized orbitals(Fig.1). Energy Original atomic orbitals sp hybridized orbitals Fig.1.sp Hybridization of carbon
Section A – Structure and bonding A5 SP HYBRIDIZATION Definition In sp hybridization, the 2s orbital is mixed with one of the 2p orbitals (e.g. 2px) to give two sp hybrid orbitals of equal energy. This leaves two 2p orbitals unaffected (2py and 2pz) with slightly higher energy than the hybridized orbitals (Fig. 1). Key Notes In sp hybridization, the 2s orbital and one of the three 2p orbitals are ‘mixed’ to form two hybridized sp orbitals of equal energy. Two 2p orbitals are left over and have slightly higher energy than the unhybridized orbitals. For carbon, each sp hybridized orbital contains a single unpaired electron. There are also two half-filled 2p orbitals. Therefore, four bonds are possible. Each sp orbital is shaped like a deformed dumbbell with one lobe much larger than the other. The remaining 2p orbitals are symmetrical dumbbells. If we define the 2p orbitals as being aligned along the y and the z axes, the two sp hybridized orbitals point in opposite directions along the x axis. Each sp hybridized carbon of an alkyne can form two σ bonds using sp hybridized orbitals. The remaining 2p orbitals can overlap ‘side-on’ to form two π bonds. Alkynes are linear molecules and are reactive due to the π bonds. The nitrogen and carbon atoms of a nitrile group (CN) are both sp hybridized. The carbon has two sp hybridized orbitals and can form two σ bonds, one of which is to nitrogen. The nitrogen has one sp orbital which is used in the σ bond with carbon. Both the carbon and the nitrogen have two 2p orbitals which can be used to form two π bonds. Related topics Properties of alkenes and alkynes (H2) Chemistry of nitriles (O4) Electronic configuration Alkynes Definition Geometry Nitrile groups 2px 2pz Original atomic orbitals sp hybridized orbitals sp 2py 2pz Energy 2s 2py Fig. 1. sp Hybridization of carbon
A5-sp Hybridization configuration has which. the es two orbitals e between th or pl nt 2pan and an to pair up.This lea are possible Geometry The 2p orbitals are dumbbell in shape while the sp hybridized orbitals are deformed dumbbells with one lobe much larger than the other.The 2p,and 2p. orbitals are at right angles to each other (Fig.2a).The sp hybridized orbitals occupy the space left over and are in the x axis pointing in opposite directions (only the major lobe of the sp orbitals are shown in black;Fig.2b). A molecule using the two sp orbitals for bonding will be linear in shape.There are two common functional groups where such bonding takes place-alkynes and nitriles. Alkynes Let us consider the bonding in ethyne (Fig.3)where each carbon is sp hybridized. The C-H bonds are strong bonds where each hydrogen atom uses its half-filled H Fig.3.Ethyne. 1s orbital to bond with a half-filled sp orbital on carbon.The remaining sp orbital on each carbon is used to form a strong c carbon-carbon bond.The full o bonding diagram for ethyne is linear(Fig.4a)and can be simplified as shown (Fig.4b). a >G )H—C—c—H Fig.4.(a)Bonding for ethyne:(b)representation ofabonding. Further bonding is possible since each carbon has half-filled p orbitals.Thus,the 2p,and 2p,orbitals of each carbon atom can overlap side-on to form two n bonds (Fig.5).The r bond formed by the overlap of the 2p,orbitals is represented in dark
Electronic For carbon, the first two electrons fit into each sp orbital according to Hund’s rule configuration such that each orbital has a single unpaired electron. This leaves two electrons which can be paired up in the half-filled sp orbitals or placed in the vacant 2py and 2pz orbitals. The energy difference between the orbitals is small and so it is easier for the electrons to fit into the higher energy orbitals than to pair up. This leads to two half-filled sp orbitals and two half-filled 2p orbitals (Fig. 1), and so four bonds are possible. Geometry The 2p orbitals are dumbbell in shape while the sp hybridized orbitals are deformed dumbbells with one lobe much larger than the other. The 2py and 2pz orbitals are at right angles to each other (Fig. 2a). The sp hybridized orbitals occupy the space left over and are in the x axis pointing in opposite directions (only the major lobe of the sp orbitals are shown in black; Fig. 2b). A molecule using the two sp orbitals for bonding will be linear in shape. There are two common functional groups where such bonding takes place – alkynes and nitriles. Alkynes Let us consider the bonding in ethyne (Fig. 3) where each carbon is sp hybridized. The C–H bonds are strong σ bonds where each hydrogen atom uses its half-filled 1s orbital to bond with a half-filled sp orbital on carbon. The remaining sp orbital on each carbon is used to form a strong σ carbon–carbon bond. The full σ bonding diagram for ethyne is linear (Fig. 4a) and can be simplified as shown (Fig. 4b). Further bonding is possible since each carbon has half-filled p orbitals. Thus, the 2py and 2pz orbitals of each carbon atom can overlap side-on to form two π bonds (Fig. 5). The π bond formed by the overlap of the 2py orbitals is represented in dark A5 – sp Hybridization 15 sp z sp a) b) x x y 2p 2py y z y 2pz 2pz Fig. 2. (a) 2py and 2pz orbitals of an sp hybridized carbon; (b) 2py, 2pz and sp hybridized orbitals of an sp hybridized carbon. HCCH Fig. 3. Ethyne. H H H C C a) b) C C H Fig. 4. (a) σ Bonding for ethyne; (b) representation of σ bonding
Section A-Structure and bonding mm头o bonds. Nitrile groups can be used to explain the bonding within a nitrile group C≡)where both th evel diagram in Fig.6 shows how the valen electrons of nitrogen are arrang ion A lon air of elect sone of the,but rbital can be and 2n bitals can be bonds. s the onds of HCN a lines and how itals rwo元b Pi Bond Fig.5.-Bonding in ethyne Energy Original atomic sp hybridized orbitals ig.6.sp Hybridization of nitrogen Pi Bond(x) Fig.7.-Bonding in HCN
gray. The π bond resulting from the overlap of the 2pz orbitals is represented in light gray. Alkynes are linear molecules and are reactive due to the relatively weak π bonds. Nitrile groups Exactly the same theory can be used to explain the bonding within a nitrile group (CN) where both the carbon and the nitrogen are sp hybridized. The energy level diagram in Fig. 6 shows how the valence electrons of nitrogen are arranged after sp hybridization. A lone pair of electrons occupies one of the sp orbitals, but the other sp orbital can be used for a strong σ bond. The 2py and 2pz orbitals can be used for two π bonds. Figure 7 represents the σ bonds of HCN as lines and how the remaining 2p orbitals are used to form two π bonds. 16 Section A – Structure and bonding C C H H 2py 2pz 2pz 2py C Pi Bond (π) C Fig. 5. π-Bonding in ethyne. 2py sp 2s 2px 2py 2pz Original atomic orbitals sp hybridized orbitals 2pz Energy Fig. 6. sp Hybridization of nitrogen. C N H 2py 2pz 2py 2pz C N C N Pi Bond (π) Fig. 7. π-Bonding in HCN
Section A-Structure and bonding A6 BONDS AND HYBRIDIZED CENTERS Key Notes aand x bonds Every bond in an organic structure is a o bond or a bond.Every atom in a structure is linked to another by a single o bond.If there is more than one bond between any two atoms,the remaining bonds are bonds. Hybridized centers All atoms in an organic structure(except hydrogen)are either sp,sp'or sp' hybridized.Atoms linked by single bonds are sphybridized,at ns linked by double bonds are sp'hybridized*and atoms linked by triple bonds are sp hybridized.* Shape Hybridized centers are tetrahedral,p hybridized center onal and sp groups bridized Reactivity is weake Related topics sp Hybridization(A5) (*with the exception of allenes R,C=C=CR2) andπbonds owing rules: all bonds in organic structures are either sigma()or pi()bonds; all single bonds are o bonds; all double bonds are made up of one o bond and one bond; all triple bonds are made up of one o bond and two bonds. Fig.1.Examples-all the bonds shown are bonds except those labelled as. Hybridized centers All the atoms in an organic structure (except hydrogen)are either sp,spor sp hybridized (Fig.2)
Section A – Structure and bonding A6 BONDS AND HYBRIDIZED CENTERS σ and π bonds Identifying σ and π bonds in a molecule (Fig. 1) is quite easy as long as you remember the following rules: ● all bonds in organic structures are either sigma (σ) or pi (π) bonds; ● all single bonds are σ bonds; ● all double bonds are made up of one σ bond and one π bond; ● all triple bonds are made up of one σ bond and two π bonds. Hybridized centers All the atoms in an organic structure (except hydrogen) are either sp, sp2 or sp3 hybridized (Fig. 2). Key Notes Every bond in an organic structure is a σ bond or a π bond. Every atom in a structure is linked to another by a single σ bond. If there is more than one bond between any two atoms, the remaining bonds are π bonds. All atoms in an organic structure (except hydrogen) are either sp, sp2 or sp3 hybridized. Atoms linked by single bonds are sp3 hybridized, atoms linked by double bonds are sp2 hybridized* and atoms linked by triple bonds are sp hybridized.* sp3 Hybridized centers are tetrahedral, sp2 hybridized centers are trigonal planar and sp centers are linear. This determines the shape of functional groups. Functional groups containing sp2 hybridized centers are planar while functional groups containing sp hybridized centers are linear. Functional groups containing π bonds tend to be reactive since the π bond is weaker than a σ bond and is more easily broken. Related topics (* with the exception of allenes R2CCCR2) sp3 Hybridization (A3) sp2 Hybridization (A4) sp Hybridization (A5) Hybridized centers σ and π bonds Shape Reactivity C H C H C C C O C O CH Cl H H3C O CH3 CH2 H3C CH3 CH H3C 2 CH3 H3C π π π π π Fig. 1. Examples – all the bonds shown are σ bonds except those labelled as .
Section A-Structure and bonding CH cH。 CH: H.O sp° sp sp3 H sp sp Fig.2.Examples of sp.sand sphybridized centers. The identification of sp,spand spcenters is simple if you remember the following rules: .all atoms linked by a single bond are sp'hybridized (except hydrogen). both carbon atoms involved in the double bond of an alkene(C=C)must be sp hybridized." both the carbon and the oxygen of a carbonyl group (C=O)must be sp hybridized. all aromatic carbons must be sp'hybridized. both atoms involved in a triple bond must be sp hybridized. hydrogen uses a 1s orbital for bonding and is not hybridized. Hydrogen atoms cannot be hybridized.They can only bond by using an s orbital since there are no p orbitals in the first electron shell.It is therefore impossible for o r的aone are either involved in bonding or in holding lone pairs of electrons. Shape e hybridization of the a oms pres nt.Foups within them is ple,functional nal planar sp enters are planar while fur ctional groups one,alkene,carboxylic acid,acid Reactivity en more eas gous which contain,πby aldehy tones Functe of two double bonds but
The identification of sp, sp2 and sp3 centers is simple if you remember the following rules: ● all atoms linked by a single bond are sp3 hybridized (except hydrogen). ● both carbon atoms involved in the double bond of an alkene (CC) must be sp2 hybridized.* ● both the carbon and the oxygen of a carbonyl group (CO) must be sp2 hybridized. ● all aromatic carbons must be sp2 hybridized. ● both atoms involved in a triple bond must be sp hybridized. ● hydrogen uses a 1s orbital for bonding and is not hybridized. Hydrogen atoms cannot be hybridized. They can only bond by using an s orbital since there are no p orbitals in the first electron shell. It is therefore impossible for a hydrogen to take part in π bonding. Oxygen, nitrogen and halogens on the other hand can form hybridized orbitals which are either involved in bonding or in holding lone pairs of electrons. Shape The shape of organic molecules and the functional groups within them is determined by the hybridization of the atoms present. For example, functional groups containing trigonal planar sp2 centers are planar while functional groups containing sp centers are linear: ● planar functional groups – aldehyde, ketone, alkene, carboxylic acid, acid chloride, acid anhydride, ester, amide, aromatic. ● linear functional groups – alkyne, nitrile. ● functional groups with tetrahedral carbons – alcohol, ether, alkyl halide. Reactivity Functional groups which contain π bonds are reactive since the π bond is weaker than a σ bond and can be broken more easily. Common functional groups which contain π bonds are aromatic rings, alkenes, alkynes, aldehydes, ketones, carboxylic acids, esters, amides, acid chlorides, acid anhydrides, and nitriles. 18 Section A – Structure and bonding H3C CH CH2 CH3 H3C C CH2 CH3 H3C C C CH3 Cl O H H sp2 sp3 sp3 sp3 sp3 sp3 sp3 sp3 sp3 sp3 sp sp 3 2 sp2 sp2 Fig. 2. Examples of sp, sp2 and sp3 hybridized centers. H3C C O C C O sp sp sp3 sp3 sp2 sp2 H * Functional groups known as allenes (R2CCCR2) have an sp hybridized carbon located at the center of two double bonds, but these functional groups are beyond the scope of this text.