Russian has a few rules and conventions for which vowels can be used with certain consonants.
| ы cannot follow the consonants г к х ж ч ш щ Instead, use и и is the soft counterpart of ы. |
я cannot follow the consonants г к х ж ч ш щ ц Instead, use и а is the hard counterpart of я. |
ю cannot follow the consonants г к х ж ч ш щ ц Instead, use у у is the hard counterpart of ю. |
unstressed о cannot follow the consonants ж ч ш щ Instead, use е е is the soft counterpart of о. |