In chemistry, the double bond rule states that elements with a principal quantum number (n) greater than 2 for their valence electrons ( period 3 elements and higher) tend not to form multiple bonds (e.g. double bonds and triple bonds). [1] The double bonds, when they exist, are often weak due to poor orbital overlap between the n>2 orbitals of the two atoms. Although such compounds are not intrinsically unstable, they instead tend to polymerize. An example is the rapid polymerization that occurs upon condensation of disulfur, the heavy analogue of O2. Numerous exceptions to the rule exist. [2]
| B boron (n=2) |
C carbon (n=2) |
N nitrogen (n=2) |
O oxygen (n=2) |
Si silicon (n=3) |
P phosphorus (n=3) |
S sulfur (n=3) | |
|---|---|---|---|---|---|---|---|
| B | diborenes | alkylideneboranes | aminoboranylidenes, rare [3] |
oxoboranes, rare, rapid oligomerization [4] |
borasilenes (rare) [5] | boranylidenephosphanes, rare, stable compounds are known [6] | thioxoboranes, rare [7] |
| C | alkenes | imines | carbonyls | silenes | phosphaalkenes | thioketones | |
| N | azo compounds | nitroso compounds | silanimines, rare, easy oligomerization, observed only at low temp [8] | phosphazene (P=N) | sulfilimines | ||
| O | Singlet oxygen | silanones, Si=O bonds extremely reactive, oligomerization to siloxanes | numerous, e.g.
phosphine oxides,
phosphonates,
phosphinates, phosphates |
sulfinyls | |||
| Si | disilenes | silylidenephosphanes a.k.a. phosphasilenes, rare [9] | silanethiones, rare, easy oligomerization [10] | ||||
| P | diphosphenes | common compounds such as thiophosphates and phosphine sulfides, for example, triphenylphosphine sulfide and certain dithiadiphosphetanes | |||||
| S | disulfur, thiosulfoxides | ||||||
Triple bonds
| B boron (n=2) |
C carbon (n=2) |
N nitrogen (n=2) |
O oxygen (n=2) |
Si silicon (n=3) |
P phosphorus (n=3) |
S sulfur (n=3) |
Ge germanium (n=4) |
As arsenic (n=4) | |
|---|---|---|---|---|---|---|---|---|---|
| B | diborynes | Borataalkynes have been observed [11] | Observed in ( t-Bu)BN(t-Bu) (an iminoborane) | ||||||
| C | alkynes | cyanides | Carbon monoxide (C≡O) | silynes | phosphaalkynes | Carbon monosulfide (C≡S) | arsaalkynes | ||
| N | Dinitrogen, Diazonium | Phosphorus mononitride (P≡N) | Arsa- diazonium [12] | ||||||
| O | Silicon monoxide has some triple-bond character | ||||||||
| Si | disilynes | ||||||||
| P | Diphosphorus | ||||||||
| S | Observed in (I2)2S2+2 [13] | ||||||||
| Ge | Digermyne | ||||||||
| As | Arsenic monophosphide (As≡P) | ||||||||
Other meanings
 |
Another unrelated double bond rule exists that relates to the enhanced reactivity of sigma bonds attached to an atom adjacent to a double bond. In bromoalkenes, the C–Br bond is very stable, but in an allyl bromide, this bond is very reactive. Likewise, bromobenzenes are generally inert, whereas benzylic bromides are reactive. The first to observe the phenomenon was Conrad Laar in 1885. The name for the rule was coined by Otto Schmidt in 1932. [14] [15]
References
- ^ Jutzi, Peter (1975). "New Element‐Carbon (p‐p)π Bonds". Angewandte Chemie International Edition in English. 14 (4): 232–245. doi: 10.1002/anie.197502321.
- ^ West, Robert (2002). "Multiple bonds to silicon: 20 years later". Polyhedron. 21 (5–6): 467–472. doi: 10.1016/S0277-5387(01)01017-8.
- ^ Some research has been done on isomerization of B=NH2 to triple-bonded iminoborane HBNH Rosas-Garcia, Victor M.; Crawford, T. Daniel (2003). "The aminoboranylidene–iminoborane isomerization". The Journal of Chemical Physics. 119 (20): 10647–10652. Bibcode: 2003JChPh.11910647R. doi: 10.1063/1.1620498.
- ^ Vidovic, Dragoslav; Moore, Jennifer A.; Jones, Jamie N.; Cowley, Alan H. (2005). "Synthesis and Characterization of a Coordinated Oxoborane: Lewis Acid Stabilization of a Boron−Oxygen Double Bond". Journal of the American Chemical Society. 127 (13): 4566–4567. doi: 10.1021/ja0507564. PMID 15796509.
- ^ Franz, Daniel; Szilvási, Tibor; Pöthig, Alexander; Inoue, Shigeyoshi (2019). "Isolation of an N‐Heterocyclic Carbene Complex of a Borasilene". Chemistry – A European Journal. 25 (47): 11036–11041. doi: 10.1002/chem.201902877. PMID 31241215. S2CID 195660396.
- ^ Example: Ar*P=B(TMP)2, where Ar* is 2,6-di mesityl-phenyl and TMP is 2,2,6,6-tetramethylpiperidine; see Rivard, Eric; Merrill, W. Alexander; Fettinger, James C.; Wolf, Robert; Spikes, Geoffrey H.; Power, Philip P. (2007). "Boron−Pnictogen Multiple Bonds: Donor-Stabilized PB and AsB Bonds and a Hindered Iminoborane with a B−N Triple Bond". Inorganic Chemistry. 46 (8): 2971–2978. doi: 10.1021/ic062076n. PMID 17338516.
- ^ Tokitoh, Norihiro; Ito, Mitsuhiro; Okazaki, Renji (1996). "Formation and reactions of a thioxoborane, a novel boron-sulfur double-bond compound". Tetrahedron Letters. 37 (29): 5145–5148. doi: 10.1016/0040-4039(96)01039-8.
- ^ Zigler, Steven S.; West, Robert; Michl, Josef (1986). "Observation of a Silanimine in an Inert Matrix and in Solution at Low Temperature". Chemistry Letters. 15 (6): 1025–1028. doi: 10.1246/cl.1986.1025.
- ^ Example: Ar*tBuSi=PAr*, where Ar* is 2,4,6-trisiopropylphenyl and tBu is tert-butyl; see Driess, M.; Rell, S.; Merz, K. (1999). "Ungewöhnliche Reaktivität der Silicium-Phosphor-Doppelbindung in einem Silyliden(fluorsilyl)phosphan: Intramolekulare C,H-Inserierung und seine Umwandlung in ein neues Silyliden(silyl)phosphan". Zeitschrift für Anorganische und Allgemeine Chemie. 625 (7): 1119–1123. doi: 10.1002/(SICI)1521-3749(199907)625:7<1119::AID-ZAAC1119>3.0.CO;2-1.
- ^ Suzuki, Hiroyuki; Tokitoh, Norihiro; Nagase, Shigeru; Okazaki, Renji (1994). "The First Genuine Silicon-Sulfur Double-Bond Compound: Synthesis and Crystal Structure of a Kinetically Stabilized Silanethione". Journal of the American Chemical Society. 116 (25): 11578–11579. doi: 10.1021/ja00104a052.
- ^ Allwohn, Jürgen; Pilz, Monika; Hunold, Ralf; Massa, Werner; Berndt, Armin (1990). "Compounds with a Boron–Carbon Triple Bond". Angew. Chem. Int. Ed. Engl. 29 (9): 1032–1033. doi: 10.1002/anie.199010321.
- ^ Kuprat, Marcus; Schulz, Axel (2013). "Arsa-Diazonium Salts With an Arsenic–Nitrogen Triple Bond". Angew. Chem. Int. Ed. Engl. 52 (28): 7126–7130. doi: 10.1002/anie.201302725. PMID 23740867.
- ^ Ritter, Stephen K. (March 21, 2005). "Sulfur's Turn for Multiple Bonds". Chemical & Engineering News.
- ^ Schmidt, Otto (1932). "Über den Ort der Sprengung von C—C-Bindungen in Kettenmolekülen". Zeitschrift für Physikalische Chemie. 159A: 337–356. doi: 10.1515/zpch-1932-15931. S2CID 99620074.
- ^ Hoogenboom, Bernard E. (1998). "A History of the Double-Bond Rule". Journal of Chemical Education. 75 (5): 596. Bibcode: 1998JChEd..75..596H. doi: 10.1021/ed075p596.